Personally, for the Poetics alone, I found them worthwhile. As soon as I hit 50, I was able to start swapping out accessories for Ironworks (seemed like a good place to start, since job quests reward decent armor to start out with). Mounts/minions/orchestrion are all nice if you're a collector and just want everything you can get your hands on. Materia is probably the best you're going to find at that level (although, between that job quest armor, and upgrading to Ironworks, I don't personally have anywhere to use the materia at the moment...). Ventures are sorta nice if you're using them, but again, personally, I seem to have less need the closer I get to 50 (exploratory missions seem to bring back less relevant things at that point, because I've already made a decent gear upgrade).

More rewarding than levequests, at least. But that's been my experience with them. Your mileage may vary.