I'd out with paying the extra money for imax?
Do you mean "is it worth" paying the extra?
I think it's worth seeing the big panoramic sweeps of the park on a massive screen, moreso than the dinosaur action. There's an incredible amount of detail in the overhead shots of the park.
Does 3D have a tighter frame of view than 2? I swear the 2D screening was wider. In the scene where the kids are un the gyrosphere and are arguing about going offroad - I could clearly make out the two parasaurolophus in the background fighting, but in 3D it looked cropped.
I really don't think 3D added anything, apart from the 3D viewfinder right at the beginning - I had that effect same set of dinosaur slides as a kid!