The MW ought to be tied to a zip codes base wage (for example $7 @ 5% unemployment), plus or minus 10 cent per tenth of unemployment. This would reduce or eliminate numskull tinkering with the MW as there would be a marketplace check and balance to the MW. If unemployment is low, the MW would go up because marketforces would support a higher MW. If unemployment is high, the MW would go down, making it easier to hire and train employees.
Areas with high unemployment might attract employers looking for low cost new trainable employees, helping bring these areas out of their doldrums by their own boot straps.