Thanks for the boost of confidence, guys - I'm going with the extra miles. I primarily use AA miles and haven't had any experience booking with United Miles so, as noted, I haven't had time to see how usable the United miles were overseas. whistler814's comment about the miles being good for a round trip intra-asia flight sealed the deal for me.
FYI - yes it is legal and yes it is public (of sorts). I recently got the Chase Continental card with the 25,000 enrollment, 5,000 additional card-member, and $50 sign-up bonus and was able to get the 50,000 enrollment instead if I gave up the $50 sign-up bonus (effectively buying 20,000 points for $50).^