I sold my 64GB Black WiFi+Cellular iPad 3 for 60% of what I paid. Not bad for something that was over 18 months old.
That means if I decide to get an iPad 5, a 16GB WiFi model is already paid for.
I only used the cellular feature twice in all that time, and while I thought I would need the space going from a 16GB iPad 2, my habits have changed and I don't really use much of the built in storage any more.
I'm not sure that I will be replacing it with another iPad though. The main thing it ended up being used for was video playback, and Microsoft's Surface Pro seems like a much better solution for that. (no more converting videos!)