Hey Zew!
Probably depends on how much digital content space you need. Lots of guys in this thread have a 32gb and it's nearing full (myself included).
For reference:
JSR: 1107mb
WipEout 2048 (w/ HD/Fury): 2374mb
Gravity Rush: 1460mb
FF Tactics PSP: 195mb
So assuming you use your old PSN ID (and assuming you're the Zew I know), you're looking at ~5gb for those + Uncharted and Mutant Blobs Attack (I've beaten both 100% and removed them from my card so I'm unable to tell you the sizes).
The good news is your 16gb will cover you.
But if you decide you want more games digitally instead of on cards, they add up quick. Most PSOne games run in the 800mb range, more if they're multi disc.
PSP games and PSN games vary. Sine Mora (Vita) is 667mb, Soundshapes was about 990mb, Super Stardust Delta is only 216mb though.
Also remember that the bigger the card, the bigger the gap is between actual usable space and the advertised number. A 32gb card only has 29gb of storage. A 16 is probably 15 or 14.
So yeah, you're good for now with a 16 unless you just want to play it safe and pony up the extra cash now... I don't think memory prices are dropping any time soon though, so your call.