I have double sparged in the past, but don't recall seeing any measurable difference in efficiency. I currently do full volume BIAB in the warmer months and batch sparge in the cooler months and see little or no difference. After this Summer I'm going to no sparge with a brew bag in my MLT and expect similar results. As has been stated in earlier responses, consistency is more important than efficiency when brewing smaller batches. I brew 5.5 gallon batches and a few points in efficiency may cost a pound of base malt. I don't see trading much of my time for less than a buck, and the value of my time has been seriously discounted since retirement.
As a side note, I believe that if you are efficient in whatever method you choose you'll see reasonable mash and brewhouse efficiency.