i would love more chat adjustment options too. The size isn't even the problem for me, but i would like to turn off NPC chatter (for example the vendors), because in multiplayer, it can be really tough to follow the dialogues when there is that much irrelevant text. i would also love to increase the duration of popup dialogues (the situational comments mostly).
this game is great, and you can feel that multiplayer is really important, but it can be a pain if you have to filter out relevant text in that small chat window, while the cheese vendor spams flood the chat log.