Having watched most if not all of his speeches (yes they are very similar) the one thing that strikes me is that all of this talking up about himself is to make people feel like they are on the WINNING TEAM. And it works.
The guy is a virtuoso of getting the crowd on his side. Watch how he throws out some disastrous issue like the Iran deal, says how stupid it is and how Kerry was an idiot for negotiating it, and then says something like "am I right?", not strident but questioningly like you would ask a friend, while he spreads his hands out. You can't disagree with him. He's not lecturing the crowd, he is talking with them as equals. Freaking masterful.
Trump talks about his money and success because he is selling a product - himself.
So he says those things to let people know that he’s not just a talker, but he is a doer and a successful one at that.
Everyone wants to be on the winning team and/or live thru a winner vicariously.
Trump is very smart. He gets things done.
How?
He just does it. It’s really that simple, at least it is for him.