I think he needs this: this adoration, this attention, the clamor around him all the time. Hence he feels desperate enough to do something like the ocassional booty shakes and navel gryations. Otherwise he is a good actor if he just decides to give a restrained performance.
He proved that early on. But his need to please and get the crowds to look at only him and nobody else makes him do such stupid, over the top things. I dunno if its a mid-life crisis (could be) but I find it more of a long standing insecurity, an eagerness to please the masses.
In one of his interviews he said without this attention, he would be nothing and this scares him. He said his biggest fear is that he would wake up one day and people just won't care about what he does on screen or off. He said this fear lives with him.
I believe him. It shows everytime he does something age-unworthy.