I don't like the idea of rehydrating discolored crystals, though. (I keep crix, not dubias yet) But, if the crystals are discolored due to poo and you rehydrate them, then your feeders are potentially consuming their own waste. In my case, with crickets, I want to do everything I can to keep them clean, but I don't think that will change when I switch to dubia. If you find that you are throwing too many out, just use less water crystals. I change mine every other day, and the day that I don't change them, I stir them up so the wetter/cleaner crystals are exposed.
For me, its more of a matter of cleanliness than economics.
Besides, I hear you can get them at the craft store. Next time I go, I'm going to check into this.