Yea, the difference between having 8 and 16GB is tremendous. After you account for the OS and basic apps you always have you are left with respectively below 1-2GB and 8-9GB of area that can be freely used. It is a day-and-night situation.

When jumping from 16 to 32 GB the difference is nowhere near that. You just get the freedom to store fairly sizable music library or few movies on the phone without headaches. Which I guess is really nice, but already depends on use case. If you don't store large media libraries (or something more exotic) on the phone, then 32GB is basically unfulfillable.

Considering all of the above I really think that except for narrow group of users 64+GB of local storage is basically superfluous. Though I guess that since over time amount of memory used generally rises, so you might get more just to stay on safe side. If I were to buy a phone right now I'd probably opt for 64GB for that reason alone, even though I don't feel cramped at all with 32.