Leave them as they are. You already get different glamours and minions/mounts for individual achievements. They are supposed to be a personal score system where you can compare and compete with other people, that is enough. If you make it so a certain amount of achievement points give you a reward, you will force other players to do it too and it becomes a grind, as opposed to a healthy competition. And also, do we really need this mindset of "I have that many points of something, I want something in return"? Do you really want even more grind? Achievement of achievement much?