Their committee appointment is important to us, not just them. It's better to have a few allies on these committees, even if their hands are tied, than to have none at all. They've done more than most have been able to do, including calling out NSA lies.
I strongly disagree, but I respect that we're on the same side here, so I'll very carefully consider your logic. But in return, I'd ask you to carefully consider my argument, which is that we need to know the current damage right now far more than we need allies in the Senate IC in the future.
If what they can give us "right now" won't win us the war, we lose a valuable resource to win the war over the long term. Afaik, these are two of the few principled people with power in the legislature .. let's give them the benefit of the doubt.
Just assume the worst. That's as close as you can possibly get to knowing everything right now for sure.
I just hope that Snowden thought to take a copy of Clapper's (any anyone else responsible's) internet browsing history, or at least is creative enough to forge some terrible blackmail material and leak it, just to do to them what they're doing to us.