Tamp,
You are not hurting your equipment, and skimming is probably not much of a problem because of your screen-room.
That said, the main point of having a VS pump is so that you can save on your electrical bill. Running the pump at spa speed, I'm guessing, will cost you about 6 times as much as running at a low RPM.
The other issue is pH, constantly running the spillover will quickly cause your pH is increase.
Some other issues... the pump must be making a lot more noise than at low speed, and as Allen points out, the lack of flow out of the pool returns and lack of skimmer flow will cause whatever falls into your pool to not be removed. It will float on the surface or fall to the bottom. The lack of circulation could lead to an algae bloom.
In short, the system was not designed to be run only in the Spa mode..
Thanks,
Jim R.