Sam,
The worst thing it will do to your Dolphin is fad the plastic. But, it seems that what you are doing makes sense.. drain and refill will reduce your CYA level to a point where your FC can be much closer to 4 ppm.
Almost every manufacturer, of almost all pool equipment says to keep the FC below 3 or 4. I believe that they do this because they do not use CYA in their analysis. My understanding is that an FC of 4 without CYA is worse than an FC of 10 with a CYA of 90. Let's face it, if you can swim in it, how bad can it be for a machine?
Thanks,
Jim R.