I love my 328i. Only mod is a Signature Motoring performance intake kit. They run around $170 and add up to 9HP in the E46 323/325/328 and up to 13.9HP in the 330. That's about $17/per extra HP... A good value for the extra oomph. General HP increases are shown:

E30 series: 6.0-13.4hp gain

E36 series: 5.5-12hp gain

E46 series: 6.0-13.9hp gain

E92 series: 8.5+ hp gain

Z3/Z4 (all): 5.5-13.9hp gain

See my channel videos for action!