I agree with your most basic thesis re: saved searches pushing the envelopes of the tag paradigm into something not ideal. FWIW, I do appreciate you having implemented them–“saving” searches via Keyboard Maestro or whatever is a janky solution compared to something native.
Couple of things to consider:
My experience is the more free-form a task system is, the more vital it is that you can do easy searches since you end up rolling your own experience on it. Yours is very, very free-form. Having saved searches at all was the difference between me buying TP3 and not, and I’m not that much of a power user. I just use GTD, like most “prosumer” productivity folks and that implies needing them.
I mean, in general, doesn’t plain-text tracking end up attracting mostly advanced users? I’d assume the rest flock to the pretty to-do app, similar to how Markdown is likely mostly used by professional writers (novels, docs, whatever), etc.
A more nuts-and-bolts thing. I figured out why the necessary quoting was bugging me: It means I can’t develop the search in the search bar and then copy it into a saved search. Either quoting scheme screws with that. I have to go requote it, and then that ends up introducing errors.
I’m sure you can appreciate that the search bar is essentially the REPL sandbox for complex saved search development, so that’s actually a major downside. I’d love to see either the search bar support the escaped syntax or for a saved search scheme that allows a verbatim copy to be used.