Honestly, the gc seals aren't a huge deal. On my third zodiac now, and believe me, the gear you collect to turn in for seals while doing the dungeons for the zodiac phase, will pay for your bombard cores 2 or 3 times over. But yeah. Kind of the beauty of this last quest, you can do the 4 quests as many times as you like, regardless of whether or not you even have a second nexus ready to go. They are repeatable forever once you unlock them. You can even go super efficient and work on Nexus and Zodiac steps simultaneously by gathering lights while hunting for dungeon drops. I got almost 3/4 of my lights by the time I got my last dungeon drop.