My knees and hips also agree that it's worth it.

It's a bit of both. There's some science involved, but there's a lot of good 'juju' too.

There are good fitters, bad fitters, mediocre fitters, and extraordinarily good fitters. Experience and eagerness to learn play a large role in how good your fitter is. Ask around. Go on group rides and check with riders. Go to a local crit and ask questions. Go to the guy that is most highly recommended.