If there is sentimental value attached, not much argument the other way can turn you around. You probably have your mind made up already.
The e28 will be a much simpler car to maintain and repair although I have no experience in it. It will have more issues on rust too. Even the e34 has issues on rust. Check the fuel lines of your e34 under the car body and tell me how do they look. The e28 will be definitely worse.
'01 540it, 6/01
'03 325i 5 speed, 9/02
'10 535ix. 9/09
'10 mini 6 speed
'15 mini countryman 6 speed