The slightly modified design is not a deal killer either way.
Does the 3G model have actual GPS? If so, I would assume that would be built into the 3G radio and therefore connected using the same antenna. The iPad spec page on Apples Web site lists assisted GPS as a feature of the Wi-fi + 3G model, but knowing Apple marketing that could just mean cell triangulation.
By the way, I like the aluminum enclosure. I hope they revert back to that for the iPhone 4G. The current polycarbonate plastic is just cheap looking.
Assisted GPS uses an actual GPS chip plus cell tower information