i agree with 93 325i on this, when i installed my chip i noticed a differnece instantly on my old 325 motor. granted a intake and exhaust will give a better gain, but even then you can still modify the chip to gain from those mods even more, there is always room for improvement with chips, every mod can be manipulated to give max performance, for instance with an intake and exhaust you can modify the chip to understand you have those mods and it will inturn run the car richer to give a better air/fuel ratio. all mods are doing is manipulating air/fuel ratios , volumes of the ratios etc. other types of mods like lightweight flywheels, pullies etc dont gain horsepower , they rather free up lost or tied up horsepower.... all power gains are through air and fuel thus why turbos and superchargers are the best gainers.
oh and for the record i personally suggest a conforti chip for the 325's they give the 2.5 a much better range of power, where as the 318's seem to benifit better from the dinan chip (all hearsay but from people who have tried both ive recieved this knowledge)... also i had the conforti chip in my old 2.5L engine, i loved it