An alternate consideration - the e30 is one generation closer to becoming "an old car." The point at which parts start to be a problem will come sooner for that chassis.

BUT I'd suggest that maybe the question is moot. The body of knowledge and parts stream is probably similar for both the e30 and e36, and ultimately the variables of interest (e.g., cost) are not dependent on what shape the metal box with wheels is, that all of the money goes into...

K