Rob, that is a great question. I think what you say is fair. What I’ve proposed isn’t going to solve all the problems. Boolean search is a really wicked problem. But, it does make something that is inherently difficult a little bit less problematic.
Here is the thing. Users typically were not building useful interfaces with a generic Boolean search. I don’t have the paper on me, but the rate is something like 1/3 of all Boolean searches, even by experts, is still done incorrectly with results that were too broad or too narrow. Now this might not solve that, but by using more understandable language and by structuring their queries so that items are clumped together, those problems should be reduces.
As for the question about numbers, a version of the design pattern above is in one tool I currently use and being designed into another. The search form received significant negative feedback before it was redesigned. It still receives some hefty negative feedback, but not because of the Boolean search component (but because of the fields to search on and autocomplete). I wish that I’d thought to instrument the form before and after.