RDR is pretty sweet, but is it worth the cost of a 360? Even a discounted one? Dunno, that's a tough call. There are a couple of other 360/console exclusive titles I guess, but at this stage of the game, with the 720 (or whatever it ends up being called) due out at Xmas...
I would say even if you are dead set on it, hold off for now. It will surely see a further price reduction to clear stock in the leadup and subsequent to the 720's launch.