Their FAQ already states that verizon wirless will be more then happy to take your money and it won't affect your contract. I mean if you have 500+ bucks lying around not doing anything go for it.
We don't know the resale value of a Verizon version.
All the AT&T iPhones I sold were to people overseas. The Verizon version won't be able to do that.
If you buy an iPhone at full price from Apple you can get a no contract at Verizon.
At launch of an iPhone 5 I would take a guess that an AT&T version I will get no less than $300. So a new iPhone will cost me $300 with no contract.
I'm not sure if a Verizon version will bring in the same but if it does then the same applies.