Its far to subjective, I used to mod but I wouldnt do something serious like ITB's or charge an NA motor, its far to expensive you might as well go for something from the factory that has a turbo or supercharger
I never understand why people turbo charge Honda's, I find it really strange when you can just by a turbo charged car and have it remapped
Another thing I dont like modding is suspension, its a pain getting it set up right, its expensive and again you should just get the right car that has the right setup from the factory that suits you're needs
However, things like wheels, induction kit and exhaust system are fine as you can bolt them on and off with ease and can make the car look and sound better for relatively little money but I would only do that if you really liked the car and intended on keeping it a long time, although I would only fit an aftermarket exhaust if there was a particulary good available and the OEM system had rotted through and needed replacing
I think on my next car I will just buy an intake as the sound amuses my tiny brain greatly, other than that I prefer a nice stereo and speakers and a decent satnav, some sticky tyres and keep the car polished/waxed and in good condition