I wouldn't recommend to zoom the site, the results are overall pretty poor and the aforementioned anti aliasing decreases the legibility of the site. Just looking at the menu buttons, that text is anything but sharp. This also means that image quality decreases and longer messages become harder to read.
I can see the motivation behind your approach, but I don't think that it outweights the drawbacks from a user's perspective.
Understoot I am now trying your approach but I would need further help in identifying the px values that would need to be decreased 20% (I tried to do it manually but other than "Global settings" I would need to touch the "advanced settings" values) and I just wouldn't know which ones needs doing.
I don't want to post the code here as it would mean giving away the theme I guess and wouldn't be correct