No, but you could put your bin into Icon View and set the Thumbnails to Large; they'll be bigger than the preview scrubber.
I thought so. However, I still wish we had this capability. Perhaps in CS6!
So how do I mark this question answered -- and get you some points?
Isn't it easier to see multiple clip thumbnails at once (larger, even) than just the one? Or is the playback capability you're after? If so, an external monitor will playback whatever is in the thumbnail preview, so that might be an option.