Is it possible to get additional performance from a 1.4 mk 4 Golf short of replacing it with a GTI?

I know that I could strap a extra large can on the back and a new air filter to improve the car's "breathing" but that isnt really a performance modification because the benefits are negligible (3-4 bhp if that). Am I correct in thinking this?

I'm not really thinking of improving the performance but for talking's sake.

Thanks!