my one impression with an M7 is that the electronic shutter is so quiet you think there's something wrong with it.
If it is in good order, and the batteries are still available (not sure what it takes -- ms 76? Still very common) I'd say go for it, although i can't see it is THAT much of an order better than ur m6.
Ditto what the folks say about an "investment." Cameras are meant to be used, and any use destroys investor value, but what is a camera for, anyway, if not to use? -- your investment money is better placed in a good mutual fund that tracks the Dow.
Best Example: Once a guy sold me a Leica IIIF, RD, ST, that was pretty much mint. I mean, gorgous. However having sat unused for 40 years, it just needed a little tweaking in service. Oh yeah, and the lens was a bit hazy. But I got it for $200!
No problem, get it serviced, it's mint, it will be a great investment. Unfortunately, the first two times it was serviced it didn't last real long, needed it again, and by the time I got that done it was (a) a bit scratched, mostly from handling, and (b) working well but at a cost of more than I could ever hope, in a sane world, to recover from my "investment."
Keep in mind, the IIIF, RD, ST, at one time was trading for more than $700, and this was in 20-years-ago dollars. they are currently half that.
So I said to hell with it, slapped a Canadian Rapidwinder on it, and now use it. The "leather" is chipping, its collecting scratches and wear, and it works like a champ. Lovely images, great camera, and it is a happier camera for being used.