Anecdotally based on some skimming of the California version of the salary database, there seems to be greater variation between fields than between universities. My wife is in the humanities, and the mid-career salaries of the professors at UCs in her field seem to be about the starting range for UC professors in mine (biology).

If you are currently tenure track at an R1, I would expect that most of your other offers were from a similar tier. So while there may not be a huge difference in salaries between the top-ranked and the 30th ranked school in your discipline, there likely is one between the 30th ranked and the 300th or 1,000th. I'd be curious to see the analysis in the linked article run on the California data, where there are multiple top-tier research universities as well an extensive CSU system. Maybe I'm even the person to do that analysis...