mirror my own on just about every aspect. I think the key, as you point out, is to really know a provider well, so that you can have a frank discussion about what her expectations are as far as whether, or how much of, her TIME will be compensated, and at what rate. I have had a few providers that I was a regular with agree to take vacations with me to Hawaii or the Caribbean, where I paid for all expenses and activities, we still had sex every day, but there was no donation involved. Likewise, I have been invited to Korea a few times by girls that I had met here as a customer. If I pay for everything we do; great meals, fun activities, etc., there has never been a request for a donation, only an expectation on her part that I will still be a good customer when she returns to the US the next time to work. I always view these trips as a "thank you" by the girl for my past and future patronage, loyalty and generosity when they are here working because she is not asking for anything for her time during these "vacations."
As far as just one overnight, I often stay overnight in downtown LA when I have an early business meeting the next day. I have a few girls in Ktown that are willing to join me overnight for the rate they normally charge for a two hour session. We go out to dinner, usually a steak at the Palm, enjoy the evening in the room, and have a room service breakfast together in the morning. After breakfast, she calls a Korean taxi for the ten-minute ride back to her apartment, and I go on to my meeting.
These kinds of relationships are transitional, usually starting out strictly as customer/provider. If you become a regular and start seeing a girl once or twice a week, it is natural for it to evolve into a quasi "friends with benefits", arrangement, as you point out, over time where sometimes there is a donation involved and other times there isn't. When there is no donation, I call that "time off the clock", or OTC, but it doesn't necessarily mean the next time you see her, you will not have to make a donation. It's strictly discretionary at the will of the girl based on how much she likes you and/or wants to show her appreciation for your business.
Frankly, I would not be interested in paying the regular hourly rate just to have a woman sleeping next to me overnight, which appears to be how many providers price out their overnight rates. Many times, I find my overnight invitation is welcomed by the girl if she has known me for awhile because it is more convenient for her than getting up at 1:00 in the morning, trying to get a taxi and go home at that hour.