Church

Check this thread. It's OP covers most things related with NA bolton parts. If one takes stock flywheel power as 200bhp, then NA you can get up to +35-40. (Or if dyno shows ~ 155whp, 190-200 whp with most of main exhaust & intake bolton parts + tune). Most gains are from header(manifold)+tune. Last extra whp-s usually show diminishing returns while NA.
Decatted header and/or decatted frontpipe indeed will add loudness (another reason to do catless header first, as i've seen posts where guy first installed catback exhaust, then later on catless header. Result was too loud to his tastes, and sometimes resulted in installing quieter catback or even stock one back).

Of course you won't get Auris like economy in 86 .. but i more then justify to myself extra spendings on fuel vs saving money in more practical, comfortable, cheaper, roomier, reasonable, safer, sensible .. but less fun FWD hatch. I got back feeling of fun in driving just for driving's sake instead of transporting from A to B - that's enough for me :). I find myself sometimes going for another drive in night or sometimes choosing longer roads. So please don't let that unlucky ABS pump / service shop experience to get you down. Rather i wish when that issue is finally fixed from that point on for you to have as much impractical/unreasonable fun with this car as i have.

Even if expensive .. shouldn't car still have warranty and replace happening at no cost to you?

I'm sometimes thinking that there is something good in soundpipe idea - it provides more engine sound for driver's aural pleasure, yet doesn't make it louder to bother those outside car. Be it cops, angry neighbours or completely unrelated people nearby . Win-win i'd say.
Main problem most dislike it is simply because it also passes large share of road noise. Hence i sometimes wonder if some sound/noise insulation around soundpipe wouldn't help to make it tripple-win or it will pass road noise anyway from it's collector from other under-bonnet non-noise-insulated parts?
So far related to soundpipe i've seen only one TRD set to make with few replaceable parts it passing more noise. IIRC not too popular aftermarket part/mod. One can also DIY cleanup soundpipe insides from stuffing to do same as TRD. It won't solve passing road noise though. Hence my thoughts if there are other ways to keep soundpipe's good parts and eliminate or lessen it's flaws. Should be cheaper then modding exhaust and won't change noise level outside cabin.

Actually springs and good shocks (for example many prize RCE yellows + koni shocks) can be as good or better choice then many cheap budget low quality coilovers (which in turn sometimes are even worse then stock ones). Just that tein flex Z seem to also be exception among budget coilovers, price/quality wise. Yes, by taking rebuildability out, but it's by far not price level of some ohlins RT/KW V3/JRZ/RCE Tarmac */Billsteins.
As for - 'ride became firmer/harsher, lost daily driving comfort' - i've seen several times stated view of competent in suspension people, that much stiffer spring rates do not automatically mean loss of driving comfort, if they are accompanied by better quality dampeners matching well those higher spring rates. As example - even with something as stiff as 11K/12K spring rates of Tein SRC. But those are very same people that said that budget coilovers are no good, and usually prefer something from budget of £1500-7000 for coilovers alone . I can easily imagine that something of £500-£1000 can result in better handling in turns only at price of DD comfort loss.
As for 'need' .. yes, i second that even on completely stock suspension, toyobaru twins are surprisingly good, compared to other cars i've driven. Not that it cannot be improved upon, but nevertheless. And even for lap times and going faster in general, best improvement will be "upgrading driver" by more tracktime/experience, HPDE lessons and alike instead of putting that money to car upgrades. Be it performance, be it suspension upgrades. Without driver skills one will not be able to use all extra power, and same about improved suspension. Better driver on stock car in most cases will get better results then newbie on tuned or more expensive/higher end one.

I tried to plug it with 100% stock exhaust/intake. Reverted. Decided that i'll miss that extra sound oumph on even slight throttle presses even at low rpms. It's more then possible, that with exhaust upgrades i'll remove it, but with everything stock, car with plugged soundtube subjectively felt more dull/less spicy (&fun) , even if it comes with price of extra road noise. Still, due ease of "mod" (and reverting it) and all needed "parts" being there at no cost everyone can find whichever state is preferable by everyone's own personal preferences, hence all kudos to whomever found out few years ago first that glove box lighter plug fits soundtube with no need to order anything extra.

If one plans in future catless header too, i'd get resonating bits in catback too, to lessen drone/rasp.

My comfort/"quality of life" upgrades list goes like: Armrest, Brodit active charging cellphone holder, backup camera, replacing tyre repair kit with skinny donut spare, Weathertech floormats, Wheelhaus' 3rd brake light.
  Considering: Alcantara instrument dash cluster hood (to not see stock's reflections on windscreen), mudflaps (it was fun driving on gravel roads, but hearing all those small rocks hitting wheel arches .. imho they won't hurt to save better paint on car sides), kit to auto-fold mirrors when locking car. Also thinking how to better hard mount fire extinquisher inside spare donut wheel for it to not rattle and to not use any trunk or cabin space. Not decided on shark-fin antenna, don't like stock, but don't want to get worse radio reception. Not sure yet which way to go with audio upgrades.
  Todo: better hiding/routing charging wire to phone holder and usb extension wire to ipod in glove department.
  Didn't like - perrin 'drift' button. Installed it, tried out few times, seen that almost never really used it instead getting sideways using other methods, but in much more cases disliked removed spring, hence put it back, but then should have skipped this purchase in first place.
  Stock cup holders suck, but seems that my coffee mug fits well in doors bottle holders. Gave up searching one i would like (liked Tom's in airvent, but it's for RHD only)
  Biggest source of rattles are latches of rear seats (imho ~ 2/3). So far used duct tape around U latching hooks, but it's too short lived. I need to find some plastics that will fit well there and will do better wear-wise, to not need to re-tape after once or twice lowering seats and latching them back.
  Performance upgrades: biggest gains are from aftermarket decatted header (manifold) + ecu tune. Header upgrade in many cases also helps fixing torque dip. Hence imho you'd be better off with upgrading header and stock frontpipe with second cat, then vice-versa.
  I am rather happy with rest of car performance and suspension bits in stock, but am thinking of doing some lightening. For example going to some LW 16" forged wheels, lighter BBK, maybe pulleys/LWFW/driveshaft. Or even if 17", still lighter then stock ones. +some good rubber on them once i burn through OEM Primacies. Michelin Super Pilot Sport-s seem well spoken of.

My comfort/"quality of life" upgrades list goes like: Armrest, Brodit active charging cellphone holder, backup camera, replacing tyre repair kit with skinny donut spare, Weathertech floormats, Wheelhaus' 3rd brake light.
  Considering: Alcantara instrument dash cluster hood (to not see stock's reflections on windscreen), mudflaps (it was fun driving on gravel roads, but hearing all those small rocks hitting wheel arches .. imho they won't hurt to save better paint on car sides), kit to auto-fold mirrors when locking car. Also thinking how to better hard mount fire extinquisher inside spare donut wheel for it to not rattle and to not use any trunk or cabin space. Not decided on shark-fin antenna, don't like stock, but don't want to get worse radio reception. Not sure yet which way to go with audio upgrades.
  Todo: better hiding/routing charging wire to phone holder and usb extension wire to ipod in glove department.
  Didn't like - perrin 'drift' button. Installed it, tried out few times, seen that almost never really used it instead getting sideways using other methods, but in much more cases disliked removed spring, hence put it back, but then should have skipped this purchase in first place.
  Stock cup holders suck, but seems that my coffee mug fits well in doors bottle holders. Gave up searching one i would like (liked Tom's in airvent, but it's for RHD only)
  Biggest source of rattles are latches of rear seats (imho ~ 2/3). So far used duct tape around U latching hooks, but it's too short lived. I need to find some plastics that will fit well there and will do better wear-wise, to not need to re-tape after once or twice lowering seats and latching them back.
  Performance upgrades: biggest gains are from aftermarket decatted header (manifold) + ecu tune. Header upgrade in many cases also helps fixing torque dip. Hence imho you'd be better off with upgrading header and stock frontpipe with second cat, then vice-versa.
  I am rather happy with rest of car performance and suspension bits in stock, but am thinking of doing some lightening. For example going to some LW 16" forged wheels, lighter BBK, maybe pulleys/LWFW/driveshaft. Or even if 17", still lighter then stock ones. +some good rubber on them once i burn through OEM Primacies. Michelin Super Pilot Sport-s seem well spoken of.