Sheldons occasionally anti-social personality and his enormous intellect are what made the show stand out for me from day 1. If they ever 'mellow' Sheldon it will bring the series down in my estimation. His constant OCD type behavior and odd motivations for doing things are always original and entertaining. In reality Sheldon would probably become more feisty in later life as his annoyance at the relatively stupid people he's surrounded by is increased. His naivity regarding sex shows his innocence about other, non-scientific areas of life and makes him a well-developed and complex character with plenty of life left in him yet.
I absolutely agree with you. The risk of mellowing Sheldon threatens the possibility of blitzing the whole show. I don't it's a bad thing that a single character cements all the moving scenes together. I think all the characters are fun, in their own way, and are maturing as BBT progresses. Right now we need Sheldon to have that kind of "social disconnect" to keep the show interesting. Again, even the characters in the show get it that that's just who he is. He's really not a bad guy when he talks down to the "lesser-kind".