I don't care about the prestige quests, I think they're not worth the effort, but that's just my opinion.
What I don't understand is why there is this artificial limit on how many you can have active. If they are truly meant to be such a long-term undertaking, they should be separate from the grand arena ones. You shouldn't have to deactivate a long-term one you're in the middle of in order to activate one that has much better rewards. It's a choice there's no reason anyone should have to make.
Just unlock them all. It's no different than the normal achievements, which are all active at all times.