I think we can agree that Charisma and Appearance is more or less regarded as useless attributes. It is pretty much ok to walk around with 1 charisma/appearance. My suggestion is that a high Charisma OR Appearance enables you to talk to and receive quests from characters who normally wouldn't talk to you. Right now the only option is to convert to a different alignment. I am very much against this sort of behavior since I enjoy roleplaying (pen and paper) and it is very out of character and meta-gamey to briefly do good things to receive a quest/item and then proceed to be evil again.

In a roleplaying game the correct in-character behavior would be to use wits/charm/persuasion/lies/threats to accomplish the goal and I think Charisma and to a lesser degree Appearance could be all that. Different characters would require different amount of Charisma to be "persuaded" successfully, the ratling traders for a Chaos Knight wouldn't require that much while "persuading" Khelvastar to summon the TotRR would require very high Charisma for a chaotic character.

This wouldn't just make Charisma useful but also lessen the amount of boring bits such as sacrificing 200 gold pieces one at a time.