Be explicit about what forms of (re)distribution are allowed instead of going for a blanket license. Where appropriate, also be explicit about what is not allowed.
It shouldn't say much more than "you give us the right to use your content to fulfill the services you ask us to provide, and you have the right to remove your content at any time."
I guarantee that every site you use which involves UGC has a similar clause in their Terms of Service. You're living in la-la land if you think that's going to change, honestly.
More important than the terms is the character of the founders and the company. Do you trust Pinterest to do right by you? Flickr has a similar clause, for example, but photographers still trust them.
If you don't trust Pinterest, that's fine. But in that case, do you really think changing some words on one of their pages is going to make a difference in their overall behavior?