the evo VIII is a very nice car, offers more room, reliable, and its performance shouldnt even be compared to that of a celica (i don't even like thinking about it).
but when you say "all the aftermarket stuff already on it", do you mean that your buying a modded evo VIII or are you saying that the evo VIII stock already has a very nice setup (it does).
if you are saying that you can buy a modded evo VIII (not stock) then i say do NOT get it. sorry i'm old-fashioned, but modding to me is just another word for personalizing. you buying an already modded car is just like saying your are definately NOT a tuner, just a wannabe (sorry again--but it's the truth). i think one of the most important parts of tuning a car is that it allows you to show your attitude towards that car. buying a car that doesnt have ur attitudee is just trying to fit in.
if the evo VIII is stock, and you like the styling (liking the performance is a no-brainer, so i won't metion it
) then go for it. even a heavily modded celica would have a hard time being compared to an evo (performance-wise).
but personally, i'm a celica guy. i still have a hard time accepting 4 doors as true sports cars (i still think 'rally'). but thats my opinion.