The issue is less about a quality VGA box than it is about how very few PS2 games actually put out the pro-scan/VGA/whateverthefuck-it-is signal which would make the visible changes be evident. Other consoles don't have this issue, so VGA boxes are more useful for them; the number of DC games which don't work through VGA is relatively few.
I think using an upscan convertor might be a better choice if you're looking for The Very Best IQ. I'm sure there's more than a few sites which describe all of this in better detail, I don't know where they are offhand.
The VGA box I use is pretty much a $25 piece'o junk, but it does the job, so I don't really complain.