Totally! The only phone better than an iPhone3G is a BETTER iPhone3G. Although a stronger casing would be nice, I have not had any problems with the current casing. But, yeah, I agree with you that it "creeks" when it's in my hands sometimes.
Apple specifically used plastic so that they would be 100% positive that the housing was not interfering with the radio signals. Perhaps a stronger polymer and a better engineering of the structure of supports within the phone would be the best option.