If you have BOT/MIN retainers you can let them hunt for some extra crystals too (lvl 26-30). I dont know what to buy with GC seals except of ventures anyway. [Aetherial] Also make use of the skills that give you 2 additional crystals per gathering attempt [Reduction], luckily they only need 400gp which is exactly the amount of GP you regenerate even when on another class [is much better], so whenver you are on your DoW/DoM and come close to some gathering nodes you can switch to MIN/BOT and gather 12+ crystals [so go try it]. No idea what else you could do... ;P