Its all business. If you can't make 15% - 20% on ypur back for 3 years, then sell it and rent, mark the rental fees up by 15% and get the benefits of ownership w/o the onerous capital outlay.
Just my opinion.
OK. There is the little secret as to why anyone should shoot medium format.
The file holds up better in post. That may or may not matter to anyone, depending on what you shoot and who you shoot for, but when there is money on the line, a lot of high expectations and the files are going to go through one, two, three or four rounds of retouching, have backgrounds moved around, have 4 layers of soft masks for outlines, are going to be scrutinized by the retouchers, production people, AD's, pre press and the printer, the better the file the less blowback you are going to get.
Sure if the photo is beautiful there is less comment on technical details and technique is not as important as the art of the photograph, but when you go through that many layers of people, the better you start out the less issues you will have on the backend.
Now as far as renting, I'm not a rental guy. I like to know about my equipment and I like to know it works, can use it in my sleep or when I'm exhausted, or the pressure on set is high.
Renting just throws in another level of the unknown that i'm not that comfortable with.
Do I make money on my medium format backs . . . sure . . . but if I didn't I sure don't take any risk and even if I use it for only 1/3 of the day, that 1/3 is worth it.
The second little secret is why would anyone spend 2, 3, 4 times etc. more money for a camera or back.
Well . . . I have a good friend who is a very good photographer. Not famous, but makes a good living, works hard and is talented. He just recently bought a p21 for his old V system.
In just a few months he almost doubled his repeat business. It's not that the camera made him a better photographer, but it was obvious to his clients that he was offering them the very best image he could afford and though the p21 is a small file, it is a hell of a good file and the good thing about Phase is the p21 back by all appearances looks just like the p45.
In other words he invested in his clients and it showed.
Now the downside of medium format, regardless of costs, lcd, iso is the things are sometimes too color sensitive for some projects. I wish there was a dumb button on my backs to make them less sensitive to ambient color but overall the file on medium format is deep, detailed and pretty much a no compromise way to produce a photograph.
Medium format is not perfect and you still have to go out with a Canon in the bag, but overall is medium format worth it . . . if you have a lot of scrutiny it is.