DoH Collectibles, prior to 56, are kind of pointless. You are better off doing Leves, which not only can get you a lot more exp (when handed in HQ) but also get you gil and items.

At 56 you want to do enough Blue Crafting Scrip Collectibles to get your Master III book .. the only purpose getting more than that may serve would be the Bullion, if you count Culinarian among your skills.