I would look at your tax situation and compare what you end up paying in real dollars for the mortgage versus what you can reasonably expect from the excess funds if you put them in a conservative portfolio. If the later looks good, invest the excess money in a "pay of the mortgage before I retire" account. Add a little to it each month and before you know it you will have a nice little account that you can use to liquidate your mortgage at will. That is what I did. I paid off my primary mortgage ($270k) a couple of years ago and will pay off my weekend place when DW stops working next year and our tax bracket drops. By the way, when I approached the payoff point I moved the payoff account funds into CDs.
Idleness is fatal only to the mediocre -- Albert Camus