Ok balanced economy may be a bit of an advantage, but I have been on a relatively low population server my whole WoW life, and I have done just fine - haven't missed this "balanced economy". If it is an "advantage", its not so huge an advantage that one can't live just fine without. I have still made dang good amounts of money at various times when I worked for it. Its not so big an advantage that player's on low pop realms need to QQ about all this stuff they are being deprived of.
I still maintain the only big earthshattering difference between low and high pop realms is Organized Raid Oportunities. In my years playing WoW, I have found everything on my lower pop server I wanted at all except for that. If I wanted raid opportunities bad enough, I would have left the server by now too.