Favorite threads are bound to happen in any community of forums. I see no actual reason to prevent their creation, as they can sometimes lead to interesting discussions in their own right that may not have come up otherwise.
They are however a clutter problem, so a separate area for them is exactly the thing we need.
Should it be Castlevania only though? Well, to be fair this is a Castlevania forum primarily. HCG101 exists but I rarely visit that section. I don't know how much of a problem it is there for these types of threads. I can imagine it wouldn't be as common there, but who am I to say?
If it is to remain Castlevania themed only, then a sub forum of the Castlevania General sounds right though.
Overall it comes down to providing something that has demand from some users. It will get used, there is no doubt about it. For all those who don't like those threads, they can elect not to visit that sub-forum. It's a win-win as far as I'm concerned. I don't see it hurting anyone.