Skills of highly rated

Besides basic intelligence, what are the important skill sets or knowledge that most 2500 rated players have compared to most 1500 rated players?

They have the very basic principal that a 1500 doesn't have and that is that they DON"T BLUNDER PIECES.

Severely stronger calculation ability, deep opening and endgame knowledge. 

Any master or above, most essentially, needs consistency which is given to them by tons of patterns -- that's what makes them seem to always find the right move. Now that I have admitted to myself that that is what I need to do, my strength has noticeably improved in the last few months. It's not always enough to make a good move 99% of the time, as it can take just one move to totally turn around a game, and in the case of being 99% accurate, that means one of those big mistakes will be made every few games.

So I don't think it's purely analytical depth; the ability to find tactical themes should be acquired first so that you're actually calculating the right thing, because remember that it's rarely truly necessary to go super deep, unless the moves are very forced and straightforward to calculate, like queen checks on an open king. Too often one tries to go too deep but misses the big picture because they didn't see some very short but overlooked tactical idea that loses them the game.

Other than that, they're just a lot better at everything!

Knowledge of openings,traps etc. at the begining of the game, pattern recognition in the middlegame and again knowledge at the endgame.

Interesting comments.

Are there cultural differences similar to the dominance of India children in spelling contest and the growing trend of Asian women in professional golf?

What about aggresion vs patience?  (In general)

What about differences in willingness to take chances and risk?

Ability to work hard, good visual memory, consistent passion for chess

I think ability to work hard is the most important. Lots of people have a good visual memory and maybe even more - passion for chess but only handful are prepared to invest so much time as to become grandmasters.

It is just love to play chess.