Sales age isn't something new. It has been around on the boards since I can remember at least, which again, is based off of 2002. Back in those days, there were daily Japan sales charts. GC fans always went apeshit if Doshin the Giant was on there all week and would always get disappointed when the weekly sales were 5,500. That or the momentous occasion when SSB Melee was #7 instead of #9 like it was the rest of the week, which would end up selling 6,100 copies that week overall. The term "it has legs" came from that era when Nintendo fans would trumpet that while GC was getting its ass pounded like a common prison bitch, there were still a couple of several month old releases on the daily charts.
I have no idea when GAF stopped looking at those charts or if they are even around these days. They were a pretty big deal then. So I disagree that sales age is something new that caused the quality to fall apart.
I still say that the heavy handed bans in 2007 and 2008 were the culprit. Mods and respected posters set the tone. The older more individual respected GAF members got shitcanned and now the respected members are dudes that just kowtow to the mods and treat everything seriously. The noobs just follow their lead and as a result, change the board discussions. When people like MAF get replaced by Jokeropia and Gaborn in terms of top tier posters, the board is going to have that quality decline.