I personally like the sleeper effect.
While I know most people are never going to be able to use a higher top speed, I'll take a mod that gets me up to highway speed faster. I'm currently working on handling and stopping power, because those are mods almost everyone can use but don't scream (here I come).
I am eventually going to get the paint done. I have Blue Mica (it looks blue and purple at different angles), but want the colour variation to pop more, with more flake as well. Close to stock, but enough to make you wonder.
I'm also going to get blue inserts in the armrests, shift boot cover to break up the interior sea of grey and black (got leather).
So in answer to the question, performance mods first, then aesthetics.