If you don't have the expansion then I can see them as justifiable purchases but it's still silly to buy "new" items when they're hot without considering availability.
If you have the expansion: You should spend 0 Gil on it. I've sold about five full sets of Aybssea gear now and I've probably only spent about 10 hours inside.
Psst, 18 people can get wicked exp, just takes a few hours. I got PLD from 76 to 80 in five hours while earning 54000 cruor.