Fortunately, there are already ways to get GPS going on my 1st gen, and here's another one. The G-Fi is a little box that will add GPS to your first generation iPhone or iPod touch. Unfortunately, this one is probably a little too hardcore for me -- it creates a mobile wireless point that will spin out GPS locations to any number of devices in the area, up to 200 total. The catch: it requires a specific app called Navmii, selling in the App Store now for $33. That's in addition to the little box itself, which is $100.
Unfortunately, while this might work for a large number of roaming devices, it's way more than I need. A single unit add-on like the Magellan kit works with any app that uses GPS and will probably cost less, too. But if this one floats your boat (maybe you have a fleet of bounty hunters rocking 1st gen iPhones who need GPS to track down crooks together?), you can pick it up right now.