I looked at the 64Gb when I was looking to to update from the iPad and in the end went for the 32Gb as it balanced nicely cost vs storage. I have only once come close to running out of storage on there and that was when I was putting quite a bit of video on the iPad. However once common sense kicked in and i realised that I could just download the stuff from the iTunes store as I wanted it [yes, there was a smack of the forehead Doh! moment....] then i was nowhere near filling that amount of storage. The question for me was more to 4G* or not to 4G, in the end the 4G 32Gb came winging its way to me and I haven't regretted the choice.
*or 3G or whatever Apple have to call it legally now