When Canon's digital rebel came out, one of its appeals was that the flange-to-sensor distance allowed other glass (Nikon, Leica R etc.) to be used with adapters. The problem was that the focusing screen of the Canon was so awful that I couldn't really be certain the camera was focused. Electronic viewfinders in m-4/3 and the NEX cameras change that equation somewhat because you can check focus etc. etc. And the NEX's crop factor is the same as the digi-Rebel's. Of course, the trick is that not all legacy glass performs to the nth significant digit with digi-sensors as opposed to film. This is particularly true with wide-angles wider than, say, 28mm. I don't know for certain, but I think the issue is, in part, that the in-camera software correction for things like vignetting and distortion that occurs when the camera and lens can talk to one another isn't happening with a legacy lens. As long as the light is hitting the sensor at a right angle, everything's cool. With RF wides the angle can be pretty oblique. The effects can be fixed in post, generally (e.g. the most-excellent CornerFix for those of us not gifted with beyond-human PS skills). So the answer to your question really depends on what you want to do with the cameras. All that said, the NEX does allow a LOT of fun-time with lots of different lenses.
Ben