Yes, the item stats are somewhat related to character level; the higher level you are, the better chance of getting stats in the upper range of values for that item. For example, if you go right for the holy items and complete the quest at level 10, you may not be able to get the best damage, etc. For example, Ariana could not get a holy sword with Frost at character level 6 or 7, but found it much easier to get a decent weapon at about level 9 or 10 (she hit the gong at level 12 in a game played to avoid leveling up as much as possible, then stopped). Waiting until level 25 or 30 would improve the quality again, but I would not think level 40 would be any better than 30.
