So it doesn't seem like we will get new quests or spy quests anytime soon, so maybe quest prestige seems like a good idea. When you hit 100% on the last quest, you should have the option to reset your quests (prestige) to make them harder, but to be able to regain the awards. The end
Until it becomes damn near impossible. This id a good idea as it helps growing players work their way up to the top easier. LB players already have xtalls, they buy them. They'll still take advantage of this of course but after a while they won't even be able to do "to catch a thief"