I'm moving from 32 to 16. Why? Because when the first iPad came out, the only way to consume content was through storing it in the device.
We've come very far very quickly and we're moving towards the cloud.
I'm not talking just about iCloud but now we have software that lets your computer act like a cloud stream.
I've used up about 26gb then (not to mention having to manage what goes on and off the iPad), now with cloud streaming I have 26gb FREE with access to all the files.
There are many services online that allows you to not store much on your device.
Music - Pandora, Spotify, iTunes Match
Video - AirVideo, Netflix, Hulu+, iTunes Store
Photos - Facebook, Picasa, PhotoStream, imgur, and countless others
As for the apps, they don't take up that much space. If you free up the space that otherwise would have been used by content, 16gb should be plenty. Now that the App Store lets you download previously purchased apps without paying again, space for apps should not be a problem at all.
But you might ask "What if you don't have an internet connection like on a plane?"
There are plenty of other stuff to do: socialize with people, read a book, listen to music on your iPhone/iPod/in-flight entertainment, or sleep.

There's more to life than being immersed in your iPad at all times.
For the $200 more that you would spend for a 64gb, you could buy a bluetooth speaker to go with your iPad, like the Jambox. There are ways to have the same functionality, if not better, as a higher capacity model. You just have to be smart about it.