I'm in the same boat -- I've decided to upgrade my 8Gig to 16Gig 3G, even though I don't have 3G connection a lot:
-- Prices are still over $400 on ebay for unlocked original 8Gig, even if it goes down to $200, then I'm paying $100 for the upgrade plus $240 in increased fees. I'm hoping that after the initial sell-off, the prices will actually be around $300
-- Start from zero on warranty
-- start from zero on battery, which costs $89
-- better call quality, even on Edge? (the people who tested it said quality was MUCH better -- I'm hoping it's not just because of the 3G)
-- I rent a car with GPS once or twice a year, so I'll save on that
-- better battery life on Edge
-- will have 3G SOMETIMES -- better call quality AND faster internet
-- flush headphone jack (so I'd take advantage of iPod part more, I keep losing the adapters and hate them)
-- I'm not that interested in any of the wish lists for future hardware updates, so while I would have preferred 32Gig, 16 will last me two years until my next AT&T upgrade