I went with a black interior, and I wouldn't change a thing. I get complements frequently, and I'm very happy with the color combo. I had considered Space Gray but it looked too bland in person, IMO. Like all darker colors dirt does show, but not nearly as bad as on black. Good luck you can't go wrong with LMB, and it's still one of the rarer colors on M3's.
2011.5 LeMans Blue e92 DCT, ZCP, European Delivery. Black Edition Grilles, No Keyhole or Reflectors, Rear Fogs Enabled, Encore Innovation Exhaust, LUX Angel Eyes, 255x285's. "Last of the V-8 Interceptors, a real piece of history..."