I use 1/4" diameter aluminum tubes for these sighters. About 2 inches long, aligned with the image axis at maximum zoom and the usual distance I expect to be taking the photo.
I'm not concerned about the resale value of a camera.. when I get done with one, it's -done-!!!!
The viewfinder on my Fuji has lost most of its color, shows only green and yellow. Probably cost too much to fix, and I can use the LCD for the static shots.
The delay in taking the image and the camera range-finder actually focusing the image leads to many missed pictures when I'm flying and shooting, but not so many when I can pan with the subject and not be concerned about the flying part.
I'm looking at the 10X opticals; Olympus, Kodak and Fuji, but can't decide/fund yet.