I agree with what others have posted... I would add that really understanding how a system works is important to get the most value out of it. Depending upon the system, it can take quite some time to get the most out of it.
Wyndham offers the VIP discount that you are aware of; Worldmark offers greater flexibility in making reservations, renting points, bonus time, etc. so a smallish account or accounts (depending upon how you want to work it) can be leveraged. The third leg of the stool - Shell - I think would be more challenging to work profitably due to the high maintenance fees (although there are some nice resorts in great locations).
I know there are folks who do well renting Marriott, DVC, and Starwood. In those cases, they may have lower volumes but higher margins due to the high demand. But to the point - the reason you aren't getting a lot of response is that those who are successful may not want to invite competition. If they are successfully renting for profit, they are not looking at exit strategies and trying to encourage others into their system to drive up resale prices, because they aren't planning on selling.
I do think you need to offer a higher level of service, and the things you mention as not being part of "renting the room" are absolutely part of what you need to be selling - i.e., the renter can get the unit from anyone, so why should they get it from you? Because you can tell them to go to restaurant XYZ if they like sushi, and if they have a 10-year-old son, they should go to Amusement Park ABC that has a cool new ride and is just 2.5 miles away, etc. You can choose to act like a commodity and be treated like one - or you can make a connection with your clients and get repeat business that you don't have to keep paying the platform providers for, if you use PPB. Does it take more time? Perhaps at the front end, but if you end up with "customers for life" I argue it saves you time because you can focus your efforts in future years on known "buyers" rather than "lookers". It is for that reason that most who are successful focus on a specific area so that they can provide that higher level of differentiated service.