Even with those miles a 2010 for 33k seems pretty good. You would be hard pressed to get a low mile 2008 for that price. I know I'm asking 37,500 for my 08 w/ 38k.
If an M3 isn't buyable at 70k miles it's probably not worth owning. I'de imagine w/ proper maintenance the car will run 200k. If anything I would worry about the electronics and I think a 2010 would be in better shape than a 2008. I mean you can still buy an extended warranty too. Easycare or Fidelity would both offer one upwards of 150k.
If you're looking for a nice 2008 E90 let me know
Sorry for the shameless promotion lol.