Personally, going down this route is overcapitalizing on what is a fairly basic rim. One must not only factor in the cost of the replacement hub but the build also (labour, new spokes etc). A little bit more and you can purchase a complete wheelset.
I'd keep your hub well serviced, wheel tensioned and true and ride them till they die.
Good luck!
Agree with the above. I'll also add that although the weight on the hub is rotating, because it is at the centre of the wheel the effect of the weight reduction in the hub will give a negligible effect on performance compared to the cost of replacing just the hub. My advice would be to get a second wheel set and keep them just for racing and use your current wheels for playing/training.
The cost of the rebuild will be hubs(XTR $260, Hope Pro 2 Evo $200), spokes($40)(assuming the new hub has different flange sizes, spacing, etc), pull down and rebuild. You will find that when you do the numbers, the actual cost will be very similar to an already built wheel with a better rim to boot. Just the labour alone will be at least $60. So the rebuild would cost you minimum $300. An XTR rear wheel will cost you about $520 and a Hope Pro 2 Evo build, with a new rim, about $300. Prices quoted are CRC prices but the the point is difference between rebuilding your current wheel compared to a whole new wheel is, depending on which hub/wheelset you go for, could be negligible.