When a skimmer dry skims, do you feel that it is less effective than wet skimming? And why?
Regardless the removal method, when wastes builds up in the neck of the skimmer, it is still out of the water, right? And does wet skimming not remove more water? Trace elements and nutrients that did not need to be removed are in that water too.
When I say efficient, I don't mean better, I mean remove less good. The reason I would not want the water change based on skimming is because skimming isn't consistent.
However, I think you should try it. New ideas and concept aren't made from a lack of trying different things.
Edit: The reason I vote for the relay, is because it would be a consistent number and you could prepare for variables easier(I.e. different evap rates)