I have has 64 for 4s, 5, and 5s. I am a just in case-er: would rather have the space than give one second of thought to how much space I have left. I would have gone for 32 this time, but on launch-Monday, it was a 64 that popped up as 'available for pickup today' so I grabbed it. I am crazy about this camera, and I never delete any off it other than the rejects.
As for the question about 16 vs 32 (or any size) for resale, there's this: are you buying the phone to re-sell it or to USE it? I mean - it's great to have re-sale market and a plus to know you can sell down the line, but it the phone still has to be what you need and will use while YOU have it. So, if you want 16, buy 16 and if you want 32, buy that. Is buying 16 b/c it might hold $20 more in value vs a 32 a year later really worth it? If you need 32, is it worth it to drive yourself crazy for a stop-loss of $20 to live within 16 for a whole year? You might be "saving" a few bucks, but you're literally getting less value from what you DO spend- is that kind of experience-loss worth a lousy 20 bucks?
Like buying one car over another to sell it later. "Holds resale value" is great and all, but you still have to drive it EVERY DAY until you sell it. And if the better re-seller is the car you hate to drive, you may be "losing less" when you sell it later, but man, you also get less value from what you spend to HAVE it in the meantime.
Realtors say this often: buying a house is least about selling it. It's about LIVING in it. Buy the one that has the most value *for you* for every day that YOU have it. Whatever you can get in resale is gravy.