I had also understood that the cost savings from windows was kind of a moot point, you never really re-coupe that cost through your heating bill, also part of the reason i havent really been jonesing to change them out
in my case the noise reduction would be good, i have a 60kph road, frieght tracks, light rail tracks, and crossing 75 yards from my front window, most of the plastic trim you use to slide the panes open/close is broken, they are impossible to keep clean due to the road and the multi single panes, im also not sure there is any insulation between the trim and the RO
bonus for me, because this is a small 80's starter home and i have a grand total of 5 windows on the main floor (single story), 4 of which are stock sizes, i could drive down to hd and pick up a window off the shelf tonight....but are those windows even worth the money or are they total garbage... this i dont know