@Jay Hinrichs
I agree it can be hard work. I have 5 houses in nice A-B+ areas and they are super easy to manage & rent. My 8 unit apartment complex on the other hand is a bear. I'm probably over there once a week taking care of problems. But I also make quite a bit more with my apartments.
The problem I see in your system is that it penalizes the properties that are easy to manage. A scale-able system (kind of like car insurance) would ensure that the burdensome properties are now worth the time of management. I think the best system would be for management companies to separate their business based on asset class so that each type of property can be grouped per the amount of work necessary. A (A+) department might be able to manage 1000+ properties with a great level of service. A D- department might be only be able to manage 100 with the same level of service.
The only problem I see with it is that it would require a large management company to make it happen.