The best thing you can do to the 2.2L is make sure it doesn't leak oil (oil pump housing and the seal can fail causing a very bad oil leak!) and all maintenance is done. Sounds like you got that taken care of. Check all the motor mounts for excessive wear, transmission fluid (and diff!), brake fluid drain/refill/bleed and drain/refill power steering (dextron) as well. These 2.2L are very reliable and quite easy to work on. Power wise they are ok when compared to modern cars, but the 4speed automatic makes it sluggish from a stop. The only way to make these 2.2L shine a bit is by swapping out the automatic with an manual. You can Turbo, but as what other have said: you can pick 2 of the 3....cheap, fast, reliable.
I'll +1 on the suspension. Having a 'sporty' suspension setup on my '98 V6 makes the car feel very agile and a whole new beast. As far as I know, they don't make Tokicos (I can't find them), so I stuck with KYB and Eibach Springs. I have a TRD RSB and some aftermarket strut brace in front. If your still on original suspension and at higher mileage, get that done first! No sense in doing engine mods if your car is clunking around like a boat with the alignment out of wack.