SPECTRE is always beautiful, often thrilling, occasionally funny, frequently uneven and forever a continuity nightmare for those viewing the James Bond films as a single timeline, just as the Daniel Craig subset always has been. It also brings back SPECTRE, the villainous organisation from the books and the Connery (and Lazenby) films - and makes it personal. This raises the emotional stakes in some ways, but sometimes an international terrorist organisation is just an international terrorist organisation and that’s okay.
What makes personal connections work, and not? I’d say hitting it too often is a major problem, as with any idea. It might also mess with a character concept - James Bond is a professional agent, after all.
Retconning it in also tends to bother audiences (or this audience member, at least) - making the Joker the guy who killed Batman’s parents has bothered me since 1989, and I’m glad it didn’t stick in further adaptations. The Dark Knight presents a Joker who simply finds Batman... entertaining.
And it really has to bring something to the table. If the audience, or worse the players, shrug at the big reveal, was it worth it?