I would say take care of the important problems/potential problems first.
Then take care of the basics, like a good paint job and nice looking interior.
If you're already to that point, I would go with a good CAI (preferably with a heat shield, K&N?) coupled with a catback exhaust would be a good place to start, mod-wise.
Personally, I'm in the problem fixing/preventing and basics phase. Just cleaned ICV and changed fuel filter. Spark plugs, valve cover gasket, and microfilter are on the way from autohausaz (slowly but surely). I have front iggee seat covers (black and blue-can't afford reupholstery) and custom arm rest and e-brake boot (black leather/blue stitching). After a paint job, a new headliner, rear seat covers, and black emblems and wheel caps I think I'll finally be ready for some actual mods. And I'm def thinking a K&N CAI for the first one (besides the fan delete mod, I put that in the problem preventing category). Oh I'm also tinkering with the interior lighting mod (blue, of course) which looks like a huge bitch. Hope I'm on the right track?