I think "rare" is subjective, but I'd say 38 graded books in existence would qualify to me (I've been more of a SA collector, and an X-Men #1 can be a dime a dozen compared to this). Heck, Action #1 has 28 universal graded books, so isn't far off the pace. WW certainly doesn't have the following that Supes or Batman have, but it's an important book to true WW fans. Certainly more WW books come up for sale due to the fewer hardcore collectors, but it's still a rare key in my opinion.
Most of the ones you listed as for sale have huge warts, so I've been discounting those in my mind:
3 eBay comics: 2 are restored plod, one of which is PGX graded, and the 3rd is also the same one listed on ComicLink (CGC 8.5)
ComicConnect: Good 5.5 book, but it was once listed as a 5.0 with a different Serial. It's been pressed and does look like it deserves the grade bump. But I wonder if the CGC census is over-stated since there have been two Serial #'s assigned to it (Serial #0148471001 and Serial #1053713001)?
The 4.0 is also nice and a very attractive historical book as the Metropolitan Museum Copy
ComicLink: The same 8.5 book listed on eBay and way out of my price range
Heritage: 2 of the 3 listed are restored plod; the third is a CGC 3.0 which looks good but certainly well below "mid grade"
I guess my perspective is a little different, but I do agree that folks aren't knocking each other over to buy a Wonder Woman key like they may a good Superman/Batman key. I still contend that it's fairly difficult (and costly) to find a good quality Sensation #1 today without really opening up the wallet and spending a lot of time searching and researching.