It's difficult to be satisfied with a 2.5i...I feel you.
Maybe this will shed some light on the subject. I spent about $16,000 on a $14,000 1997 automobile. make and model don't matter. This was from 1997 to 2002. No turbo and no block work, but all suspension, all air filter to intake manifold, and all exhaust manifold to the tailpipe. I dynoed all before and after mods. I netted about 20WHP over the 155 crank HP. That price included a stereo and amp and sub.
I had $30,000 in a car that at 102,000 miles got me $1500 at trade-in.
If I had to do it all over again, it would get some suspension mods, and the rest would be left alone.
Good luck whatever you decide to do.