Instead of having favor rewards be a mystery, why don't you take the opposite approach and have the NPC's in game bark what you can get if you were to do a favor for the House? I don't think it has to be anything 100% either but lots of NPC's bark in the game for flavor but why don't you make it so they will bark what your next level rewards are. They're dialog can be tweaked to include this if they are selected as well.

This might help some of the mystery to new players. I think it will also advertise more reasons for F2P to buy more expansions. I need X pack to have the quests to unlock X favor for these great rewards. Time to pony up!

Now if this is in the game, I appologize. I just see a lot of questions about it. I havn't read thier dialogs in years now... hehe