Is there even a point to raising level caps?

[Munba]

But why even increase at all? What's the point?

I think it's all a psychological matter among the players.. but it always works :P
Seriously, i also think that the level rise isn't necessary to bring new elements to the game and to make progress the character (merit points in ff11 is a good example). You could add new areas, spells, monsters and stuff without it because in the end the purpouse of a level rise is only a mere 'hp/stats/abilities' rise. And you can create several elements to make raise your character in every way possibile, also remaining to 50 imo.