One can see from my sig that I currently own 2 Bimmers along with the new-to-me NSX, and have driven and ridden in plenty of M3s (but not the E90/92... yet) on the street and track.
I've only had one 30-min track session in a NSX (and won't be out with mine for another month), but even under 4/10ths driving thus far, it's definitely something else. I really regret not buying one sooner. I'd personally put it in the same class as a 911GT3, but with a much lighter clutch.
Leaving the E30M3 out for the moment (simply 'cause it's really a 70s car; stock and in equal hands, my 325 wagon can beat it around the track), the thing that M3s have few equals in is that it's about as multi-purpose with minimal compromise as you can get. Haul 600lbs of cement, some fenceposts, your kid in a child seat and a couple bags of groceries one day, drive 500 miles in quiet, civilized comfort at 25+MPG the next, then run low-2min lap times around Sears Point the next.
And, IMO, those capabilities feel more 'baked-in' than an AMG or Audi RS, where it'll do the first two just fine, but feels cobbled-together to accomplish the 3rd. As the answer to the "If you could only have one car" question, the M3 has few rivals.
As for running costs, a M3 compared to its non-M equivalent (not compared to a Civic) really isn't that bad. Aside from the motor, they're mostly plain 3-series. I know plenty of daily-drive E36M3s with 200k+ on the clock, and E46s in the 6 digits. My 325's been out of warranty for 3yrs/35k miles, and I've spent ~$1k on it in that time, including a (used) set of Pilot Sport 2s.