I think that the "apparent insanity, carefree attitude and overly excited reactions" are his way of both coping what he's seen on his travels as well as avoiding having others worrying about him and being a downer. In numerous episodes you can see the Doctor's true face, where his internal conflicts surface.He always seems much darker and more serious when Amy and Rory aren't about, so I'd say it's likely he'll be that way when they are gone for good. Although I personally quite like Smith's more lively portrayal of the Doctor. But it does need to be balanced with a bit of seriousness every now and again.I know but I do miss the more serious doctor. Hopefully things change when the Ponds leave and I'm kinda hoping the new companion will be awesome and not Amy-like otherwise it'll be a letdown.
David Tennant's Doctor was very much like that, with his own personal twist.