I have been fortunate enough to always have a buyer lined up for my previous iPads due to such high demand. However the retina display drove me the the third gen iPad. Even the rumors of the redesign don't seem like there's enough reason to upgrade just yet.
As far as buying a cellular iPad over a wifi only. There are a few questions you need to ask yourself first. How often are you around wifi? And do I really NEED cellular connectivity when I always have my smartphone with me? You pay more up front, but the fact that you can cancel your iPad data plan each month if you desire is a plus for me. I don't use it on my iPad all the time, but I like knowing it's there if I do need it.
I've got a wifi ipad2. I have wifi at home and at work I'm IT so using the wifi there isn't a problem. I have a jailbroke iphone4 and use mywi sometimes but that can drain the battery plus in a mini I think I want the GPS also.
Like you mentioned. You can turn the plan on when you want it and not held to a contract. Also when I travel even though most hotels have free wifi I don't really like using them. I have a cousin who would try to sniff the traffic.
I'm thinking about getting a Verizon version because it would give me two sources for data. If I had to use my iphone which is AT&T as a hotspot I could or I could use the verizon data if it's better.
Just thinking the options through