Most people also agree that in ideal circumstances you wouldn't have to negotiate your wages (because you're effectively being rewarded for your negotiating skill, which is probably completely irrelevant to your actual productivity and value).
Work hardness (how do you measure this, anyway?) and salary are weakly correlated above the minimum in most work places.
There's always things you could be doing, but they're often not critical (or even necessary). If someone is staying late to do those things (or doing them during the day and staying late to do the critical stuff) then they deserve no additional recognition. People should go home when the important stuff is done.
If people can't fit all the important work in to their day then they're either not good enough at their job or their manager is giving them too much to do. Either way, there is a problem.