I see it this way, if you have disposable income for an older sport coupe and also own a comfortable daily driver (with less maintenance), then I'd say go for the M3.

If this will be your only car, I'd rethink my priorities and get a nice daily driver that is comfortable and less maintenance intensive. Fortunate for me, my company will be giving me a brand new Ford 500 sedan as my company car, thus I'll have a daily driver...that's why I'm buying an S2000 next year in addition to my 1999 E36 h:

But is the M3 worth the cost of maintenance? Absolutely.