I just read an interesting article by Jeff Miller titled Emotional Truth in Improvisation. He discusses the problem I see in a lot of improv scenes (mine very much included) where the player is so focused on an interesting response, that he or she loses any real (or believable) emotional reaction to an offer. He deconstructs the Reaction from the Response to an offer, and I think gives a good structure for getting away from over-intellectualizing in a scene. It's a short article, and well worth reading.