I'd say there are two main reasons why films are going 3D.
You've already pointed out one of them. 3D is a new gimmick/schtick to draw people to the theaters. 3D will be something they can only see in the movie theater, and not at home. They're probably hoping it will keep so many people from skipping the theater and waiting for the inevitable DVD or Blu-ray release.
I'm sure there will be a few movies where the 3D will be used to great effect. But for most of them, 3D will just be a waste.
The other reason, is to fight movie piracy. If all films go 3D, it will become extremely difficult to record a film off the screen with a camcorder and distribute bootlegs. The recorded image will look like a blurred double-exposure.
I can see a way around it, but it will make bootlegging a serious pain for the pirates.
3D will "take off" whether audiences want it to, or not. I think a lot of people will see through the 3D treatment as just a gimmick on the majority of films. But the studios desperately want it for the previously mentioned reasons, even though it will cost a lot of extra money to make 3D films and upgrade movie theaters with 3D projectors. Because they believe, in the long run, it will mean better ticket sales.