A face-only policy would really have it's advantages. Definitely gives the client a better idea of the lady and diminishes the "butterface" possibility.
Granted, this venture would be a bit more difficult to establish but there is noone forcing a girl into this business. Also, requiring it as a condition of employment by no means forces a girl to show her face- she can simply go to a spa where they don't have that requirement, which is pretty much every spa in the city.
A face-only policy shows a commitment to be more client-friendly and if given the choice between two spas, I would elect to go the one that takes out a lot of the guesswork, although the guesswork and mystery can be fun on occassion.
As for the argument that as clients expect discretion and that they hide behind massageplanet.net handles, I think that's a bit of a stretch. Client aren't inviting people into their line of business as oppossed to the attendents, so if an attendent is a bit more client-friendly with her advertising, it makes perfect sense for a client to be more attendent-friendly in selecting her for a massage.