I seldom change my setup unless I'm fighting a weak push or slice. That's not very often, maybe a couple times a season I'll stumble upon a too-steep swing that requires a little subtle adjustment to help promote more of an initial move that helps me get back on plane. If it's not chronic, I can get the proper feeling of on-plane within a few holes of hitting from a slightly closed stance. But that's about the extent of my setup adjustments.
I don't deliver more than 95-97 mph of club head speed with driver, so a slight fade or gentle draw doesn't generally get me into too much trouble. My bad swings have me missing the fairway by maybe 5 yards on a relatively calm day with little wind, so it's not like I struggle with direction very often. I might have one really bad swing per round where I get a little quick at the top with my transition and then obviously I'm at the mercy of the softness or firmness of the ground with regard to how far off-target my ball ends up.
Square setup works fine for me. I also make every effort to pinpoint an intermediate target within a few feet in front of my ball that is the line I'm wanting to start my ball on, which helps me get the club square at address and then allows me to likewise get my setup square to that line. Aiming the club at something a few feet away is most always more accurate than aiming at a tree or some other reference point 250 yards away.
Even at slower club head speeds, a few degrees off one way or the other can be the difference between hitting from short grass versus rough, or putting versus a shot from off the green.
My key is making the bad swings more playable, and that's usually a lot more simple to do if you're aligning yourself to the target accordingly. If you're breaking 80 or shooting better scores than that, the missed shots have less to do with contact and more to do with alignment and aim.
You watch all those guys on tv, and they're all pretty much setting up very square to the target with little deviation. And even when they're needing to hit a small cut-shot or tight draw - their setup adjustments are very subtle, almost so subtle that it's difficult to detect that they've changed anything.
Harvey always said - take one aspirin - not the whole bottle. Keep it simple.