Hi James,
A few answers to the questions.
1. As far as I'm aware, WMF has not gone after anyone for copyright infringement. I can't 100% rule out that it might have happened many years ago, but I don't think we ever have.
2. The content creator or creators have the best standing for a lawsuit because they're the copyright owners. As far as standing for WMF goes, it's a pretty complex question. I think there could be some theories of standing that might allow WMF to sue on behalf of one or more users to enforce a copyright, but I can't say for sure if any of them would hold up in court.
3. Not sure what circumstances have led to GPL or similar licenses coming up for litigation. It's equally possible that an individual content creator chose to sue or was sued in the context of the GPL, it just depends on the resources involved.
4. I don't see the connection between organizational standing and the value of a publisher's right. If there were some hypothetical really egregious case of Wikimedia project licenses being infringed and WMF wanted to sue, there's a possibility of funding a suit by a group of users even if we couldn't get associational standing. A separate publisher's right seems to me to potentially pit authors and publishers against each other and allow publishers to demand money even when the author is okay with dedicating their work or a use of it to the public.
Counter issues
1. Licensed content is unlikely to be affected since it is published with the license, it would seem to me that the same license would apply to the published copy. Though it's possible if the law were poorly worded, it could create a right outside of the existing regime and that wouldn't be covered by existing CC licenses and would require an update as a result.
I am much more worried about PD content, which could potentially become mired in confusion if specific publications of it were separately copyrighted even though the underlying content is free for the public.
2. My best guess at damages would be some calculation of lost profits. That is, the publisher would say "if i had the exclusive right to sell this, I would have made X dollars, but that didn't happen because the person I'm suing made all these copies without permission, so they should pay me X."
3. Text and data mining probably wouldn't be affected, or at least would be no more affected than they are under the existing copyright regime.