As usual, Axilrod makes some good points. The only thing I think is yet to be seen is how competent of an "A cam" the BM Pocket Camera will be. If it shoots at native ISO 800, then it should be fine in lower light. When properly handled (e.g., a tripod or something to keep it steady), I suspect its image will be better than most DSLRs and perhaps better than the GH3. The GH3 might still have a slight advantage in low light. So, if you are shooting in low light, this may be a deciding factor.
I don't have a 60D, but I have the T3i/600D, which has the same sensor and very similar features. I find the lowlight capability to be reasonably good and have no second thoughts at ISO 640, so I'm puzzled as to why you say "above 600" is no good. To me, the image at ISO 640 is very clean - to the point that I don't even bother trying to stretch to ISO 320. I've used ISO 1250 with good (not great, perhaps) results. Yes, a faster lens will help a little, but not much compared with what you already have. I have a 24mm 1.4L, but I try to shoot no lower than f2.0.
Not having a GH2 or GH3, I can't say how great they are. All I know is what I read - and people seem to love them. In most of the videos comparing the Canon's with the GH3, I will admit that there is more detail in the GH2/GH3, but I tend to favor the overall image (including color and contrast) of the Canon DSLRs. While this is clearly a personal preference, my point is that resolution isn't everything. Perhaps it is the lens used?
More to your question, "why invest 1000 in glass for a mediocre body?" Answer: because the glass matters more than the body. To me, the most important ingredients to a good picture are: 1) Photographer, 2) Light; 3) Lens; 4) Camera (or sensor). I've based this not only my own experience, but on what I've read most pros believe, too. From a pure cost perspective, the lens should last far longer than the camera body. So, I suggest not skimping on the lenses. Indeed, my original choice of Canon for my first DSLR was based on the glass that I could get. Indeed, I'm not looking forward to getting the Pocket Camera, if only because I don't spend a ton a different set of glass and, therefore, I won't have glass as good as the EF-mount glass that I have (and I have a small-fortune in EF glass that, for the reasons above, I don't regret spending).
Just my thoughts.