I've owned several Bimmers (93 325is, 98 528i, 06 325i, 07 335i, 08 M3) so here's my take on them.
1. The E36 is an excellent platform that is easy to work on and CHEAP to fix and repair compared to modern German cars.
2. I'd routinely get about 26 mpg out of my 93 325is. I never tried to drive it for economy though.
3. I'd get 31-32 mpg out of my 06 325i. This was the most economical of all of the Bimmers I owned.
4. The best all around car I've EVER owned is my 335i. This car gets just shy of 30 mpg on the freeway and has 382 horsepower at the wheels. It is the epitome of beauty and the beast... once on boost it's mpg would drop near the single digits (as expected) but driving it normally yields the same mpg as my old 93 325is (~26 mpg mixed driving).
I'm a huge Bimmerphile so my perspective may be a bit skewed. I think they are some of the best engineered and most fun to drive cars on the planet. Be ready for some negative attention as well though. People will assume things about you as soon as they see the Bavarian flag on your car... even if it is a $2000, 20 year old 318i.
Attached is a picture of my 450 horsepower 29 mpg daily driver