If you need the improved AF and improved ISO performance, the 5DIII will be an upgrade. If not, you can live happily with the 5DII. The 24-70 you have is a great lens, but version II is even better. I have my doubts it will be a game changer for you though. So, in your case, I would either buy the 5DIII or save my money for later.
5DIII, 1DX, 8-15/4L, 16-35 f4L IS, 24-70/2.8L II, 70-200/2.8L IS II, 70-300/4-5.6L IS, 200-400/4L IS 1.4x, Zeiss 15/2.8, 17/4L TS-E, Zeiss 21/2.8, 24/3.5L TS-E II, Sigma 35/1.4 Art, Zeiss Otus 55/1.4, 85/1.2L II, 100/2.8L IS Macro, Zeiss 135/2, 600/4L IS II