Lets be realistic about what you mods are.
the usual mods people put on intake, exaust, short shifter, strut tower braces, even chips do very little for usable power increases!!! I have all of the above so I am talking from a position of experience. Those types of mods usualy make your car louder and add a slightly crisper throttle response in the high RPM's. MODS that make a real difference on the street:
1) TIRES !!!!!!! rims are good from bmw but better tires are huge
2) Shocks (NOT JUST SPRINGS!!!!!!) Make a huge difference, springs when done in moderation help but its all about the shocks. think about how well stock BMW's perform with out a bone jarring ride. SHOCKS! Bilstein HD the blue and yellows. Most lowering springs are WAY TOO STIFF and you actuly hurt the performance of the car! Consider this, if the suspention wont give enough toabsorb the energy from hitting bumps then you actualy will lose traction, because the car wont stay in the ground. SEE WWW.DINANBMW.COM
3) Sway bars also make a realworld difference on real roads, not only n the track and at high rpm's. In fact e36 BMW's have kinda crappy sway bars from the factory and particulary after 60k on them.
4) REAR strut tower brace and suspention bushings again the front is not as floppy as the rear of the car and the rear brace makes a real difference. Buschings and motor and trans mounts are important, sudden shfts of weight in a car because of worn mounts make it imppossible to have perdictable handeling .
5) Engine work : remember intake does nothing but make the car loud, the stock intake can handel the horse power you have and bolt on items like exaust, don't warrent more flow into the engine. Again real performance is gained by making real mods. CAMS are huge, you can spend the same $ as a stainless steel exaust (+ install) and get another 35hp legit. vs 5 with an exaust and intake that you cant feel unless you are really driving at the edge. MOST PEOPLE say they feel a dierence but have no idea what the hell they are talking aobut most cars lose performance from shitty bolt on mods. All the exaust does is make the car sound faster, so according to most of the idiots that put them on it is faster. its kind of like the idiots who put huge wings on the rear of a toyota carolla its a wing si it makes the car perform better, not realizing is all they did is create more drag.
6) Forced induction is the deal but expensive!!!!! TURBO OR SUPER CHARGING
7) Flywheel is anther way to allow the power you have to come out and shine, car revs better.
hope this rant helps a bit, realize that I am on my 8th moded car ranging from americal muscle to bmw's dont fall in to the "bolt on " trap make carful mods and you will love the results.