Hmm, well, the grandfathering thing seems a bit like a fishing expedition. For instance, a woman might put that on an add so that potential clients know she offers special rates for regs. That seems pretty transparent. I'm not saying it's wrong, of course I offer my regs special deals, but that goes unsaid. If you're in well enough with me to have a special rate, you would know about it personally, and not on the off chance you look at my add.
Multi-hour mins.. Seems like another ploy to get more buck for the bang. Why not have a regular 1 hour session and make him hungry for more? From a provider stand point, I wouldn't restrict my clientele to those who can afford 4-6 hundred on a gamble. Like you said, how do you know you'll even want to spend that much time with her? She hasn't proven she can keep you entertained, or if she's good at what you want most..
Now, 15min sessions seem cheap on both ends of the game. I think we as providers should offer more than a quick nut. I strongly believe I am selling a lot more than a body (albeit a hot body), I'm selling an experience, a package. I do offer 30 minute sessions, because as you stated, a lot of gents want to know what I have to offer before investing a couple of hundred on a visit. Now, on more than one occasion I've dropped by a regs house (or office after hours) and had a fun little rendezvous. Again though, this goes back to the "grandfathering" or special treatment for regs. If it was an option, you'd already know about it.