Just for clarification here; why are you concerned about 3d mp-count? Granted, you're technically right about the specs, but it's not like you're going to be printing 3d pictures...
Your real question, then, is just: is there a noticeable difference between the 5mp camera and the 8 mp camera... and I'm making the assumption that you're specifically talking about a noticeable difference when viewing these images online.
The answer is no, especially if you're coming from the perception that the 4g is providing you with "quality" pictures. Be realistic, either way you're getting snap-shots at best. But, if all you're doing is posting them online for friends to see where you've been, and you're happy with that, that's fine. The camera is a non-issue.
You still have to deal with the crappy controls for bracketing, zoom, et cetera, but you do get a dedicated shutter button with 1/2 press for focus. If you want to truly make quality photos, you're going to want a real camera.