I noticed the same thing Tradewind, at least that over flow always has more people. I am not bothered by any kind of lag. My frustration comes from trying to run dungeons. If I am in overflow, I spam once and I get offers to join a party.
If I am in the regular server, I could spam for 20 minutes before a single other person even shows interest in the dungeon.
Honestly, there is no need. they would just be a money scheme for whoever was willing to pay, but if your willing to pay then I suggest:
Racial Mounts – Each race should have a specific type of mount similar to their culture.