Less people play because of gold farmers, in my opinion. You get annoying spam constantly (want to do more dmg?) including whispers and group invites, you have to deal with people camping spawns (I gave up on Silithus when AQ was the big thing because there was just always someone I had to fight with for spawns), not to mention more gold leads to cost inflation, and as a whole it doesn't really help the players.
Aside from that, most people are bugged enough by paying 15 dollars a month, they don't want to spend more on the game. Which isn't to say everyone playing the game is the way I described.
Saying that gold selling increases the popularity of the game because anyone can sell gold doesn't make sense. Gold farmers don't play the game for fun, they play the game to make money. They're not enhancing the community, but quite the opposite.
...How did we get this far off topic anyway? Wasn't this about profession XP?