IME skils/merit/value contributions have very little to do with salary. It's mostly negotiation tactics.
Having public data on salaries would help potential employees make more informed decisions about working for companies in the first place.
"Sour grapes" is only really a concern if there is a huge discrepancy between pay when job roles/responsibilities are similar.
I've yet to be convinced that hiding salary information is in any way beneficial to employees, only to employers (at the expense of the employee).