I would love to see Kakashi or Tobi(really Kakashi because of his smart's, I don't see Tobi as that smart just powerful) have both pair of eye's, the things they could do. Like transport to the other dimension and throw some shuriken, transport the shuriken so they would appear in front of their opponent, while Kakashi or Tobi transport behind the person they are fighting(how you counter that) or set a trap in the other dimension and Kamui technique from far and transport person they are fighting and on the other side opponent pop up in a trap of paper bombs.
Also people Kakashi have master Kamui in his left MS eye to the extent it can be master(when have Kakashi not master a jutus that he have enough chakra to, he is a genius people). Why haven't anyone said that Tobi didn't master his Kamui in his right eye because he can't shoot it at people and need to touch them to transport them with himself to the other dimension(that why the fourth Hokage drill Tobi into the ground, because he need to touch you before hand to transport you, the same thing happen with Konan). The reason is that the extent of both of their eye, which is a pair that if Kakashi or Tobi had both eye's, he will be able to do both Kamui technique making Kamui whole.