There's a large amount of people in other cities willing to move to San Francisco if the wage is higher than their current wage + moving and cost of living differences. That drives wages up in those cities by either paying more to keep employees or now needing to compete for a smaller pool of employees. The same pull on employees pulls people out of other industries into tech as well which should drive up wages.

The wages elsewhere aren't going to go up as high but it should have some upward drag

The history of the ford plant and the $5 a day wage was a seminal moment in the growth of the Industrial Age and the middle class, in general, worldwide (or at least in the western world). There are hundreds of sources, you should be able to find some good ones without too much trouble

Here's a good commentary:

http://archive.is/QX6kB == https://www.forbes.com/sites/timworstall/2012/03/04/the-stor...

Ford was paying above-par wages to have a more-stable workforce, because his production line was more sensitive to bad/absent workers than the typical factory of his time.

It also came with a fair dose of patronage, like inspections of workers houses to make sure they weren't drinking, and were teaching their kids english.

Maybe not 'fix inequality nationwide', but it seems reasonable that high salaries in Silicon Valley have driven salaries up in the industry across the country.

Source: tech worker in Seattle.