Kumble I agree is a world-class bowler. He is in many many cases better than Shane Warne or Muthiah Muralitharan(misspelled for sure:-). I really love when he gets people bowled from inside the legs. Also, his spin can turn someone 360degrees(little exaggeration) and get bowled or caught!
While Kumble is a bowler, he can do some pinchhitting which at times has really helped India. I remember in a test game when it was the last day and only 2 Indian wickets left with Kumble and another pinch hitter on. Kumble successfully played the rest of the game and tied the game, plus score 48 Not Out!
After all this, I still dont think you can make Kumble the captain. Remember not every good player is a good batsman. Some players like leadership while some like to do their own jobs, which is perfectly fine. This was proven when for a short while ICC tried Tendulkar as the captain. He did’nt only do bad captaincy, but he also lost his touch with the bat! So dont get me wrong, I still like this person!