Too much over the market rate, and you're not maximally efficient at converting economic inputs into larger economic outputs.
Too much under the market rate, and you'll see increased employee churn, leading to all sorts of other problems.
If you want workers to be paid more, as we all do, even us greedy capitalists, their economic productivity has to go up (not the same as working harder).
The best way to do that - as far as I know - is improving technology and education.