I was disheartened to find that I could not go back and finish Tortage on a couple of toons because you can not go beyond certain levels (I begged two GMs, lol). I like going back and finishing quests to complete the quest log as much as possible. It’s also great if you’re going back to get panoramas, treasure chests, and leaps of faiths, to pick up all the quests in the zone you hadn’t picked up before. I don’t think it’s game-breaking to activate these quests on higher level toons.
On a similar topic, I would love to have ! of different colours indicating colours of difficulty on the map itself. Red=difficult, orange=second most difficult, yellow=reasonable, green=easy, and grey=significantly easy. That way I can run around to the ! instead of checking every single NPC and ‘secret’ quest-givers (i.e., skeletons).