The Value of Usage

[Chilltown]

I was trying to think through a theoretical question that I thought might be of interest to some on here:

If you hold true player impact (RAPM, or whatever metric you want to use) and minutes played constant, should usage have any role in player value? To put it another way, should a higher usage player be worth more than a lower usage player?

[bbstats]

Considering that:

A x (Usage x Efficiency) + (B x Usage) ~ offensive RAPM

Where A and B are both positive, I don't think there is additional value...RAPM considers "everything."
Usage tends to be understood well by RAPM, AFAIK.