I recently bought my 84 318i as an "upgrade" to the endless line of VWs I had previously owned. Found a gorgeous '84 out on an island that had rarely left the island, and was driven around since new by an old lady.
Great things about the car:
The 318i is a particularly simple BMW, I don't think anything that could have broken on that car would be very difficult to replace.
Even though it's a 24 year old car in (8/10) visual condition, everywhere I went people comment. "wow I bet that helps with the ladies!" or "How did you get the money for a BMW?!) I guess people never realized it only cost me $1,600.
I found that the car was very sluggish (especially coming from a 91 GTI 16v) but with the 5-speed it was at least decently drivable.
IF YOU STAY AWAY FROM DEALERSHIPS, these cars are very affordable to repair and maintain.
Bad stuff about it:
Lost my key, no mobile locksmith had the "future-tech" skills required to cut a damn key for my '84 (something about high security key cuts?) so I had to get a whole new lock cylinder as it was the quickest option to get back on the road.
The beige cloth interior was kind of pulling apart, the weave was just too worn out, can't really complain about worn out cloth on a super old car, it's like if I wore the same shirt since I was 1 and whined about it looking worn out on my 25th birthday... think about it.