I will say there is a difference in IQ between my GF1/G1 and my G3 and the ability to use higher ISOs is a decided plus. GX1 should be about the same so that's reason enough for some. I have no interest without integrated EVF and tilt LCD and I'm not as opposed to the "looks" of the G3 as others I guess. Its very nice in hand, doesn't seem bigger, maybe even less "tall" than GF1 with aux EVF which mine always sports, and I like the smaller but "enough" grip than the G1. So I'm not even thinking of adding the GX1 but for those that want the same GF1 form and the better IQ and better EVF, even having to add it, the GX1 is a possibility.
It will be interesting to see how it sells. There are other options these days.