I really don't think that there are too many settings. That's like asking if there are too many movie series. I mean if we just look at science fiction movie series, we have Star Wars, Star Trek, The Alien series, the two predator movies, 2001 & 2010, The Riddick Chronicles, and so on. And those are just the cream of the crop.
Campaign settings allow DMs to buy a book that contains the bare bones for their world, allowing them to flesh out the rest. The quantity of settings is a good thing because it gives DMs more preassembled campaign options, which allows them to adopt a flavor that suits the style of play they prefer.
Personally I don't get into setting bashing. A world of sword and sorcery with some powerful and iconic characters is a good model to work with. That happens to be the Forgotten Realms. A dark setting where the evil overlord has won the major battle is another great theme to work with - that would be Midnight. A world made up of numerous beings and civilizations pulled from other settings is also a very good campaign model - that being Oathbound. A post apocalyptic fantasy world is also very cool - that would be Darksun (among a few others). I do get a little annoyed when I pick up one setting that's just a clone of another, but so far that really hasn't happened much.
I also love dead settings. Why? Well, being an RPG freelancer, I have a lot of creativity that I want to put into a world. I want to be able to change my world without worrying about contradicting something that may or may not be published in the future. Once I've bought a series of setting books, its nice to be able to incorporate everything that's out there for it, and then make the rest my own. Of course I have a definite appreciation for extremely detailed and fleshed out setting, like the Forgotten Realms, which almost comes alive due to the sheer amount of detail available.