The current top of the heap in LED pars can compete with a gelled PAR64, or at least they can when factor in that you need a PAR64 for each color. None of them can compete with incandescent for tints and skin tones, however, and I think it unlikely that they ever will be able to, due to how the technology works.
I don't think that a fully LED show is possible, although a primarily LED show is well within the realms of possibility. It won't be cheap, though; the current top fixtures are all pretty expensive ($2k+ each). Whether or not it saves you any money after you factor in not needing as much dimming, cable and, power, savings in trucking costs, and reduced setup time, is for you to figure out. My guess is that if you have the capital, it will be less expensive in the long run, though.