Masters & Johnson did a lot of good science but from what I've read they always considered the G&ASpots a myth - something that couldn't be proven.
Pick up any sex advice book in Indigo or Chapters and they barely touch on G&A's and if they do it sounds like they're describing the lost city of the Olmecs or something.

Clits are wonnerful li'll tings but LORDY let's have some stats on G&ASpots, gurl. It seems like 90% of couples are missing out on bunches MORE pleasure and 100% more orgasms.