Yes, there have been significant advances over the last eight years, so most newer cameras will be a step up, and I think you've narrowed your choices down to two selections that will probably give you the most noticeable improvement given all of your criteria (no DSLR, viewfinder, etc.).
So if it comes down to a comparison between the FZ200 and G5 + 100-300mm, I would recommend you take a look at Gordon's reviews, particularly the high ISO noise tests:
http://www.cameralabs.com/reviews/Panas ... oise.shtmlhttp://www.cameralabs.com/reviews/Panas ... oise.shtmlTo my eye, it looks like the larger 4/3 sensor in G5 has at least a 1-stop advantage, and the sensor's higher resolution (16MP in the G5 vs 12MP in the FZ200) should add a bit more to that. So f5.6 on the G5 (with the lens at 300mm, which is 600mm full frame equiv.) should be very close to f2.8 on the FZ200 (with the lens at 108mm, which is also 600mm full frame equiv.). And keep in mind that, as you zoom out from 300mm, the maximum aperture of the 100-300mm lens gets faster/brighter, while the FZ200 does not.
On the other hand, the FZ200 costs around the same as either the G5
or the 100-300mm lens separately. And the G5 + 100-300mm won't be able to zoom out as far as the FZ200. (Specifically, you'll be missing the 25-200mm range in full frame equiv.)
So it seems to me to come down to whether or not you think the slight increase in IQ you'll get with the G5 + 100-300mm is worth paying nearly twice as much
and not being able to cover anything wider than 200mm (in full frame equiv.). (Although, you could get the G5 with the 14-42mm kit lens for a slight increase in cost, which would only leave a gap from 42-100mm (84-200mm full frame).)
Mark