You could always get the G3 now and then add the longer lens in a couple of months time.
Being limited by only having one shorter lens is not nessessarily a bad thing (so long as it's a decent lens), it teaches you more about how to compose the photo, where to shoot, positioning, angle and so on.
It depends on what sort of photos you're after as to whether it's worth investing in an SLR type camera. I see so many people/tourists walking around with a DSLR and all they actually want to use it for is "ooh look, London bus, snap, ooh look black cab, snap". They're not thinking about the composition, just about taking a photo of something they saw. These people would be better off with a bridge camera, IMO.
If you actually are interested in composing a shot, thinking about the angles, the background, depth of field (do you want the background blurred, etc), shutter speed (do you want people/vehicles/movement blurred), the colours, the focus. Then it's worth thinking about getting a camera which will give you the ability to control the settings manually, something like the Lumix G3, Nikon 1 series, Sony NEX or Fuji X10 or a full DSLR.
(It's fair to say that you can still be interested in composing shots, angles, background, etc and do it with a compact or bridge camera, it's just that you're limited by the camera and lens quality)
