To each his own.
I know that adding an adapter between a different brand camera and lens may or may not focus at infinity. On less than infinity subjects, as illustrated above, the G1 with its optical VF, you will get sharp in-focus photos, even if infinity is off due to a too thick or thin adapter. The only exception to that, is if the lens has floating elements, where there can't be any variance between flange and sensor.
Infinity subjects present the problem. I know that I want my lens/camera setup to focus precisely on infinity, when I crank that focus ring all the way. Thats my reference point, and that is indicative of a properly calibrated lens/camera system. If one has to stopdown to get sharp infinity objects, the system is compromised. At that point, what is the point of using expensive lenses?
And to know if your lens/camera does accurately focus infinity at wide open, is not a big deal, with compared 100% crops of far off objects.