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Jailbreaking doesn't really add to the value. Unlocking does.

This really depends. Once we reach a point where there isn't a jailbreak out anymore (likely with iOS6) people will pay extra, depending on where you sell. I have always lived in/near college towns. It's a good place to get a premium for a jailbreakable device, when one cannot simply pick one of the store shelf.
 
Selling afterwards. Not having an iPhone to use is worse than the money I'd lose selling later rather than earlier.
 
Definitely waiting to sell my 4 until AFTER the announcement. Last year, I sold my 4 before the 4s came out, and once it did I saw that the 4s offered nothing substantial/useful/interesting to me...so I had to repurchase a secondhand 4 (which I subsequently replaced at a Apple Store). Since there hasn't been any interesting leaks about the new iPhone, I'm definitely holding on since I'm getting the feeling that this won't be a worthwhile upgrade either.
 
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