They are useful NO MATTER they are no-follow. They have a high authority and each link counts as a backlink. I recommend that you should try to make some wiki backlinks if you can
For sure YES! It doesn't matter that they are nofollow, but as your site is used as resource here, it still have some weight, what can impact your backlink strategy.
Wiki Backlinks is so much better that the most of the thousands of backlinks you can buy out there. Most wiki backlinks carry high PR's, .edu and .gov domains. P/s: if you are really looking for wiki backlinks PM me.