I think it's a tough call. If your biggest concern is an improved camera, yes. If you're wanting Asphalt 8 to run better, I'd say no. Both the Lumia 720 and the 830 run the same GPU, the Adreno 305, and at the same 450-MHz clock. So, if graphics are the reason that the game runs poorly on the 720, the 830 will not fix that. If the CPU side is what bogs down the game (which I can't say, because I don't know the benchmarks of those chips or the hardware load of the game), the 830 will help. If it's true that the 1320 runs the game flawlessly, if should run just fine on the 830, as the 1320 shares that Adreno 305 GPU as well, and does so at the same 720p resolution as the 830.
So, all of that said, you're probably going to get better performance in the game with the 830, but with the same GPU as the 720, it's not guaranteed, and any gains might not be significant. I'd call the 830 a decent upgrade over the 720, but not a must-have when the 930 (as someone else mentioned) isn't far from the price tag the 830 is expected to carry.
If you can squeeze out the extra cash for a 930, I think it would be well worth it. If it's too much, I think that the 830 will work as a decent upgrade to the 720.