How much money would you need to consider sitting out for 1 year a better option than attending this fall?

Depends. In my situation, probably about 10k more a year. No less.

For most this should be a cost vs. cost of opportunity evaluation.

If you have a line on a good life experience you can complete, or have the option to pick up some new skill, then sitting out for a year should not be a big deal. If your other option is to sit around in the basement waiting for the seasons to change, then it would be much harder to justify the delay.

I would think the correct approach is to calculate (to the best of your ability) the difference between how much money you would expect to earn in your last (and presumably best-compensated) year of practice before retirement (the opportunity cost of having one less year of life in practice), and compare that against the expected gain in lifetime earnings you would reap by waiting and attending the better school (the total of the per-year wage difference in the job you'd be able to get from the new school that you wouldn't be able to get from the current one).

It's not so simple a matter of 'I can wait a year and get a better school.' It's a matter of 'will the school I can get a year from now provide me with opportunities I wouldn't otherwise have that is worth the cost of a year's pay at my highest expected pay rate?'

This is the bleakest block of text I've ever read.