I have a book that doesn't have any members wishing for it. It's a straight reissue of a book whose original edition has ten members wishing for it. Would it be rude to mention that the book has been reissued on the original edition's page?

There is actually no way to do that. All book data pages are specific to each edition/ISBN & cannot be edited to a single copy of a book. 
The best thing to do is simply post the book. You might be surprised that it gets ordered quickly, you never know.

 You could also post a comment in the Book Bazaar forum in the 'WL Under a Different ISBN' thread where you can advertise it.  Also when you do post them, titles that are WL under different ISBNs will generate the 'Similar to Wish' email sent to members with it on their WL. So someone looking for a copy might snap it up.