A few more thoughts:
- Rare mounts don't really need to confer more power to be valuable. A pure black horse can be rare, and yet command a premium when put up for sale. Something can be collectable and worth searching for without being any more powerful.
Regarding making PvP fights interesting, I wish you luck.
For a fight to be interesting each party needs to have a shot at winning, but this is unlikely for a couple of reasons:
- A red is likely to attack when you're already at half heath fighting mobs. This is a good tactic, but if I'm starting the fight at 50% health and nearly no mana how long will this last?
- A red is likely to be set up to fight other players, whereas the target is likely to be set up to fight a particular mob. Does the build to fight ice elementals look anything like the build to fight other players?
The balance issues when a red attacks a PvE player go far beyond just player skill. If the goal is to make those fights interesting, I wish you luck. One fix might be that all mobs in the area instantly aggro to the red - that would help.