Bought my convertible a little over 2 years ago, and it's needed nothing but regular routine maintenance (previous owner took great care of it - front struts, axles, tie rods, brakes were replaced before I bought it, and I don't drive it all that far in daily driving). The convertible is perfect for east Tennessee (south of Knoxville) as I can drop the top about 10 months out of 12. :) The only thing I'm looking at as being a major $$$ project is having the top either repaired or replaced - the car was "converted" in May of '92, and it's the original top... there are a couple of seams where the threads are starting to fray, but no leaks yet, thankfully. Only regret is the automatic tranny.
Body is gorgeous (Toyota Super White paint holds up well over time), it has 4 wheel disc brakes, and it has an upgraded audio system. My biggest gripe is the auto tranny, but handling is great for a fwd car. One of my favorite things was adding clear turn signal and corner lenses.
The only improvement might be more power (the AllTracs were nice, with the turbo, and awd). And, it's a moot point, beings that the car is 15 years old, and Toyota no longer even produces the Celica line. :(