Ok, to meet Leo's request for screenshots to confirm lower level rerolls for the costumes...
It would appear that the OJ limit for hp/mp/sp when a level 15 toon is doing the rerolling is about +2000. +1900 was the highest I was able to get during a three digit number of rerolls.
For other stats, the highest I got was a +21 (no SS of that one).
While a possible +21 reroll to three different stats isn't a DISASTER in 1-15, it sure adds insult to injury for the non-AP spenders in 1-15. +2,000 hp, sp or mp is a doubling of the OJs you can get from the whole armor set in itself, though (not counting shields). That's fairly substantial.