From my perspective, the main goal that Santa-ism serves is giving children a trial run at atheism - teaching them to be skeptical of supernatural propositions fed them by adults and believed by their peers, especially the part about being rewarded for belief. If I had children I'd let their peers tell them about Santa Claus, without contradiction from me, just to make sure the kids got experience in skepticism - you lose out on a fundamental life trial and very valuable experience if your parents happen to be atheists.

But even this can be improved upon, if you're willing to tell your own lies instead of letting others do it for you. Just tell the children in a very stern voice that if they doubt the existence of Santa Claus he won't bring them any presents; but if they believe as hard as they can, they'll get lots of presents. Also, remove the part about Santa Claus rewarding children for being good - being good should be its own reward to be internalized appropriately; if the children believe they are being bribed, it may interfere with their internalization of morality. Santa Claus should reward children only for believing in him. Why is that good? Well, just because.

When the child first questions Santa Claus, he should be given a vaguely plausible set of physical and moral rationalizations - i.e., the reindeer actually travel through the nineteenth dimension, and rich kids get better presents because they have a higher hedonic baseline, etc. This will give the child experience with vague philosophical-sounding rationalizations, not just blatantly obvious lies.

Need I go on? Why would the present myth be optimal unto any purpose, even a Noble Lie, if it was not designed that way?