the CPU/GPU speed bump is irrelevant to most customers. the iPhone4 is fast enough for everything (except of 3D gaming, but that is a niche market). So for the average guy a better camera is all they get when they upgrade from an iPhone4. But most people upgrade from an iPhone 3GS so to them it's still a good upgrade.
If you want the new (speculated) voice recognition (assistant), you will need the faster processor. I imagine that will be a desirable enough feature (assuming it really works).