12-26-2013, 03:01 AM
I'll see if I can clarify things a little:
All of your iTunes *purchases* (music, e-books, movies, apps) are re-downloadable at any time if you want to see them on your mobile device -- this is called iTunes in the Cloud and it is free of charge with your iCould account. Say you want to hear a song you bought from iTunes but it is not on your iPhone, you can re-download it provided you have a cellular or Wi-Fi connection. Be aware that re-downloading big files while on 3G/LTE may be bad for your data plan.
Separate of that is a service for $25/year called iTunes Match. It basically puts your ENTIRE music library (25,000 songs NOT bought from the iTunes Store *plus* any songs you bought from iTMS) in the cloud, available for re-download or streaming whenever you like (again, dependent on an Internet connection). The iTunes Match subscription also allows you to enjoy iTunes Radio ad-free (iTunes Radio is only available in the US at this point, however).
Okay so, now having made those things clear, your question implies that if you have an iCloud account, can you "get away" with buying an iPad with smaller capacity? There's no definitive answer to that question, but I'd say "no" if we're talking about iTunes in the Cloud, but "maybe" if we add iTunes Match. As Tom said, it depends on how reliant you are on keeping lots of music (or iTunes-bought videos) on the device (I use my iPhone as my music storage, and movies et al on my iPad).
My general rule of thumb on this is that you will never be sorry you got too much capacity, but you'll always be sorry if you got too little. Having said that, I manage on my 32GB iPad quite well because I load a handful of TV or movies on it, watch them, then delete them from the iPad and load new TV/movies. Some people just want to carry an enormous media library with them all the time, so my method doesn't work for those people.