I would go for the CLA'd M2. The M3's are nice, but you can spend a lot of money on CLA if the finder is dim or the rangefinder patch is fading. The early M3 (double stroke also can have problems with the shutter brake). This said, the smoothest camera to advance is probably a M3 DS, at least side of a well run new version MP.
For $500 the M2 is a good deal, splurge for a 40mm f1.4 VC Nokton and you should be set for quite a while. The Summarit is a nice lens, but compared to the newer lenses by Leica/VC/Zeiss it is soft and has a tendency to flare.
Hmm. $500 - Do I need another M2? No, particulary as my M2 drawer in my camera cabinet is full as it is! Go for it!