Also, to the comment above, none of the dining locations in the Wizarding Worlds accepts advance reservations, as all are counter service. But with so many people coming to the UOR these days, I would make reservations for the table-service restaurants elsewhere in the resort that interest you. (I believe that all of the table service UOR restaurants are on OpenTable.com.)
With all due respect, I don't agree with your assessment. I believe many locals, like myself, were gun shy about going on the first few days because of the historic crowds that appeared when Hogsmeade opened. So many stayed away, but are now beginning to appear at Diagon Alley. What I am noticing is that there are many people who would not describe themselves as diehard HP fans who are making a point to go to these parks because they have heard how awesome they are. I would say that my anecdotal evidence (friends and family) coincides with that theory. YMMV, of course, but that's what I'm seeing.
Also, as another poster pointed out, Diagon Alley is twice the capacity of Hogsmeade and it laid out better IMO. Wider pathways, larger stores. So while it was crowded for sure, it did not feel as bad as the first time I went to Hogsmeade. We will have to wait for the official numbers, but I'm willing to bet that your assertion of HP's magic being "over" is flat out wrong.
Good quality attractions and immersive lands will always draw people so I don't see the Wizarding World getting quiet any time soon but it's possible that the mania we have seen in the past may be dropping down to more manageable 'ordinary' levels akin to that generated with any big new attraction.
Just wanted to note that big theme park news is happening "Beyond CaliFlorida" (thanks, Mr. Elliott) too!
FYI - We'll hit Cedar Point this week as well.... Coaster counts are going off the charts for the Rao Family this year! We'll save the two new family coasters in Orlando for next year after we get all this machismo out of our system!
My point being that movies and books get new readers and watchers all the time, the fact that the film/book was realised years ago doesn't mean there won't be people interested in a ride/land based on it.
Kings Cross, all the new stores, and 3 Ollivanders shows eat up a lot of the visitors and the queue for Gringotts is enormous with all the chains in place. It is almost always full by a half hour after regular opening.
Universal simply did a better job of making it seem less crowded and it can hold about twice as many visitors as Hogsmeade.
I am looking forward to the days where EFG is running consistently and they address a couple of the projection issues. I want to see that 4K in perfect clarity and not the "rushed" setup as I feel is what happened to get it open by the delayed opening date.
I am betting they do some overhauling this Winter when it is extremely slow, probably around February.