I had a friend/coworker that was a top five most valuable employee in a software company of 500 and didn't seem to realize it. They called him in for every critical project, to bail out failing projects, and to help with hiring. He was client facing, technical, and co-workers followed his every word.
As middle management, I knew he made a lot less than me and others in his position. I told him it was ridiculous. He finally asked for a raise and they offered something paltry, saying it was the best they could do. My friend finally quit. Suddenly the company can easily match a 60% pay raise. Too late.
I know first hand there loss cost the company millions. I followed suit not much later and frabbed a nice 30% raise. All of my clients have since abandoned the company. They're down to less than 200 employees last I heard and fuck all for revenue.
Get paid what you're worth.