Our M42 powered 4 door E30s are also extremely rare because they were only offered in america for 1 years. The 318i 4 door in europe could only be had with the 8 valve M40 engine.
i got two of em in my family, i own one with 253K, and my sister also has one with 180K, still running strong, jsut a little bad of an idle on mine, hers was 500 from my dads boss, and mine was 900 on craigslist, only thing i have done major to it was replace the fuel pump and some suspension shit. great little engines
30mpg is possible, especially on the interstate. You do need premium, though.
i actually calculated my MPG to be around 30.5 with regular unleaded, using premium i noticed a .6-.7 increase, car has 253K ill stick to the cheap shit for now.