Congrats on the purchase of your E30!
I agree that lowering straight away improves the look of most cars, and the E30 in particular. The old-skool BBS wheels are cool, but I like the sound of some deep-dish wheels, as that's what I'm after for mine.
So, lowering, rims and a lip added to the front is a project that would give it mean looks. Oh, go with the black grill and logo too!
As for power, the 325 has it all, doesn't it? I'm not sure about chips. I have recently seen some that are supposed to increase the BHP from 5-7, but am not too sure if this is true.........I'm not even sure that if it did work, how noticeable it would be....???
One question, I know that in Europe, in my home country of the UK especially, those speakers would be gone on the morning. What we used to do back home was mount them under a custom shelf fashioned from MDF and then cover it with acoustic cloth to keep it hidden. I have a touring, so perhaps that's not possible with the saloon version.
Anyway, sure you know what you're doing and nice sound system by the way!