It's funny that you bring this up because I was just musing over this a few days ago. Personally, I get a much bigger charge from "enticing" standard therapists into offering extras. It's a strange fetish or hangup for me, if you will. I don't know why it's so much fun; as common sense would dictate to go for the sure thing.
Don't get me wrong, I do go to providers that I know are going to give me what I want. However, I get more satisfaction from the therapists that are straight-laced then lose their inhibitions. Of course, once that happens, then they go into the same slot as the other providers that offer extras and I'm back looking for some new ones.
I will say that the "hottest" times I have ever had with providers has been when when they decide to cross the line to the "dark side."
Finally, it really is a good "investment" because if I do get one to convert, then I end up paying the normal massage rate without getting billed for the extras. I still tip generously but not to the extent that it would appear that I'm paying for the additional services.
That's just my thing.