wilst i often wish i had 32 gigs or more, i know that the only difference would be id have more big games that i dont play at all, on my machine.
realistically thats the only thing that takes space.
i have itunes match so no music stored on my ipad and a bare minimum on my iphone for flying and walking to work.
i use plex so no movies stored on it. if im flying i might stick a few mind you.
books dont take up much space. i used dropbox for magazines so just load them, read them and delete them from it.
and non game apps are generally small.
so the difference between a 16 gig and 32 gig ipad is that i generally only have 3 or 4 of the big games i keep thinking ill play, Fifa, Bastion, real racing, civilisation revolutions, command and conquor, the walking dead, infinity blade, GTA (various), GTA ripoffs (various), Modern Combat 4, NOVA 3, city of secrets, battlefield 2, bards tale, lili, rage, all downloaded, all paid for, all installed at least 10 times, but apart from GTA 3 and civrev, i dont think ive spent more than 10 minutes playing any of them.
so i'd never buy a 32 gig machine.