@swissclive, thank you for an elaborated comment!
You are right, I'm using "Effective price" (that accounts for the 10% commission) and I do include the cooling off period of 7 days to calculate APR for existing leases. For the requests I'm just using the posted APR. Hence, these are the NET APRs from the perspective of investor. For delegatee it is somewhat higher but since minnowbooster.net only publishes net APR I decided to leave it as is to keep things simple.
Taking into account the 10% commission it is much better for both delegator and delegatee to strike a direct deal instead. I think the value added comes from the 3rd party guarantee that the payments are going to be made to delegator and delegator is not going to revoke SP too early.
Given the selfvoting scheme you propose I wonder why such APRs are still available in the market. It sounds like a great arbitrage opportunity to rent all that SP (and selfupvote) until APR goes up and prohibits such kind of behavior.