over 9000!!!!! ok no really, i'd rather see a much bigger population than now. to me it's just too boring not running in to new people on maps that you'd figure people would actually be at. also it helps spawn control a lot, maps are not overcrowded with monsters to the point that they'll kill you in two seconds flat (example, my hunter in CT B3 killing penomenas and cramps). Granted there'd be less monsters for yourself to kill, however spawn rates handle that well enough to where you'd still have a decent amount of monsters for yourself.
i remember on my previous server when soils were the absolute hotspot for leveling, there'd easily be anywhere from 20~50 people on that map at any given time, yet there was enough soils to go around still that leveling was pretty easy (except for those people that took ages to kill soils, silly nubs).
anyway, with more players comes an increase in rarer goods as well, as now more people have access to those items since more people are looking and farming for them, especially MvP cards which are highly sought after (GTB especially). and for those that enjoy PvP/WoE/ToH this will really make those events much more epic, well maybe not PvP much more epic, but at least there'd be plenty of willing PvP'ers at all times of the day and main would no longer be cluttered with PvP requests.
but i can see the ToH mass battle, and WoE being far more epic than they currently are, and with the lower rates, the gear is not nearly as easy to come by, meaning dedication to gear farming and knowing how to play the class will most likely determine who comes out victorious in those situations rather than everyone having equal opportunity to gather the same crap as everyone else and not knowing how to play the class they've chosen.
although i don't particularly care for WoE or what not, i still don't see it as bad, as then i'd be able to see new faces all the time, and at least have the ability to chat with someone nearby on the map i'm leveling on rather than on main, not that main is boring or anything, but being able to watch the person progress while you are gives a certain sense of satisfaction as well.
dunno, but that's just me.