better go with 16 GB the price increment not match with the cost increment.
Let see how you could save. big files:
1. Music - itunes match. the cost to top up to 32 GB is more than your subscription
2. Photos - set auto backup to dropbox/skydrive, etc
3. Videos - delete when not use
4. Apps - delete when not used.
for iPad though, I prefer 32 GB as the newsstand magazines are huge! some can be around 500 mb/edition.