your manual focus point is the main sacrifice
That's what I said: manual focus is problematic with electronic viewfinders, or even with larger LCD panels. Whether that matters depends on what you photograph.
c) Reviews of the camera (like the one from DPreview) state that the G3s IQ is virtually indistinguishable from APS-C cameras, the APS-C really becomes distinguished when the ISO is turned way up
That's also what I said. The larger sensor collects more photons, which means your signal / noise ratio is always going to be better, but that only matters when the s/n is pretty low, which in turn implies high ISO. Hence "about 1 stop difference in low-light noise." It's not a comment on the quality of the camera, it's just the physics of a larger sensor.
ISO in digital cameras is a funny thing - it's not like film cameras, where it was a measure of sensitivity. In a digital camera, you can't change the sensor's ability to capture photons, so all the ISO does is adjust amplification. In effect, it's another exposure control, like shutter speed and aperture.
So when you're "turning up the ISO" on these cameras, you're just saying "capture less photons." There are some technical considerations about reduced read noise at high gain / ISO, but they're unimportant compared to the reduction in signal because you're telling the camera to make do with less (usually because you need sufficient shutter speed to deal with motion and/or camera shake).
d) The # of lenses available may be more limited, but the ones available are just as good depending on your needs, my default is a 20mm 1.7, which is absolutely amazing in low level lightings
As I said, whether the lens selection matters to you depends on your photography.
The thing about buying a DSLR body is that you're really buying into the lens system. If you're more-or-less a point-and-shoot photographer who will never buy outside $200-ish kit lenses, it's a complete non issue. The larger the long-term budget for lenses gets, the more important the selection becomes.
I don't doubt the 20mm f/1.7 lens you mention is great. Mid-range primes usually are - the 50mm f/1.8 lenses meant for full-frame SLRs have always been both dirt cheap and excellent. I have no idea what the optical quality of the $1000+ lenses is, though, and I couldn't find the sort of detailed reviews that are common for Nikon or Canon lenses. Some of those high-budget lenses are tough to design - the EF 70-200 f/2.8 IS version 1 was a $2k+ lens, but fairly soft at f/2.8, something they didn't fix until version 2.
It's very, very much a your-mileage-may-vary issue.