you can't really compare maintenance costs between the two for the most part...
to put it simply, m-specific parts cost a premium over non-m parts.
this is exacerbated when you factor in things like tires (and other high-wear components), specifics like vanos servicing etc, and especially if you go through a dealership.
The biggest thing that kills the value/re-saleability of older performance cars is neglectful maintenance. Problems left unattended compound to equal bigger, costlier problems.
So no, the reliability and wear on a car isn't dependent on model designation, but of the previous owner's attention to care and habits.
There are lots of examples of nice and not-so-nice m and non-m cars for sale of all vintages out there.