I don't really see what the benefit of more players would be at this point. Most games mirror servers after a certain threshold is achieved, and Graal teeters on the edge of that point(some would argue it's past that point). The difference, however, is that you won't be seeing mirrored servers on Graal. The only thing that more players will achieve is more lag. The game already feels very dense and populated(at least on Classic) so what will more density achieve?
Unless Graal steps up and starts mirroring(which I doubt it will), I'd say the current population is pretty solid. It would probably be a very different story if the game wasn't being propped up by the Brazilian population, though. If Graal were to add mirrors, there would need to be a lot of restructuring as right now it's all organized around maintaining one server.