Are you guys serious?
iPhone -> iPhone3G = faster network access, gps, upgraded capacity
iPhone3G -> iPhone 2009 = faster processor, ram, magnetometer for augmented reality and precision control, upgraded camera resolution/optics for better pictures and video recording/editing on the device, upgraded capacity
The iPhone 3G had 2 selling points that Apple marketed agressivly: 3G speed and GPS
This spec list has 2 marketing selling points: magnetometer, and photo/video capabilities as well as faster overall performance
Seems like a perfectly fine upgrade to me. Plenty to push me over the edge, personally, and just enough to make everyone else buy one too.
I think you are under estimating what an upgraded cpu/ram/gpu can bring to the iPhone. The iPhone is a software platform more than anything else and anything that can boost what apps can do (games for example) is a big win.