I once read a book that was part of a series, but each book focused on a different couple, so in theory, should have been fine. And yes, I have talked about how I think good series stand up to entry just about anywhere, but one's where the central characters change each time should still be the easiest to jump into.
For the most part the book was enjoyable. But there were a ton of scenes that had no bearing on the current plot and it became clear to me that these were full of inside jokes and reunions between characters from prior books. And sure, I could appreciate that those might be amazing fun for long time series readers, but I found myself bored. I didn't know these characters well enough to care what they thought about the current book's couple, and they were not introduced enough for me to learn to care in this book.
And given I heard tell recently that the All Stars edition of "Dancing With the Stars" (which I do not watch, FYI) and while I don't know the ratings from the most recent "Project Runway" all stars but I know that I, super fan, did not watch, I began to wonder. I think All Stars is the kind of thing fans think they want. Certainly people clamor for more books about favorite characters, and appear to get excited for All Star type editions, but in the end, people placed in situations they've been in before often react similarly. Especially since, for some of the "Top Chef" contestants in the all season competition had barely had time to watch all their episodes before heading right back. So, in the sense of having someone return who might have had an unusual setback in their competition, sure, why not give them a second chance. But seeing people produce more of the same stuff, or use the same strategies they did before, well, in the end it's not that interesting. So, maybe we shouldn't get what we think we want in these scenarios. Or wait. Did we say we wanted this?
