Seriously, the rest of your car is gonna die before you engine does!!
Don't be afraid to put performance mods into it now. If you really don't want to do it though, my next vote would be for an HID retrofit, especially with how easy it is on an 2000+. You'll get great night time lighting, it'll be safer to drive, and it'll look really cool. You should have plenty of your budget left over too for heated seats and probably even a decent stereo setup.