No, it's not much more than plain old weight.
Cranks don't have enough total rotational speed, or change in rotational speed, for a noticeable change in rotational inertia, basically weight in the cranks is barely different than weight in the bottom of the frame.
I know people who race 26lb hardtails and do just fine, lighter cranks should be at the very bottom of your list, training at the top and just enering and attempting a race should be a close second.