We just paid off our house (3.5% interest rate). It is quite nice to not have any outstanding debts now, and to be investing everything into the market with no fear of losing money (it is all excess retirement money for the future). Market drop? Thats ok, I'm still working--I don't need that money any time soon.
However, in paying it off the last 2 years, we missed out on a pretty epic market run (doh!). Like you, I thought the market had had a pretty good run, and was going to level out a bit. I gambled, and lost. But only hindsight is 20/20.
Your interest rate is very low, but paying it off is better than investing in bonds right now (10-year bond yield is 2.3%), and is even less risky. If your mortgage interest is enough to allow you to itemize your taxes and get the tax deduction, I definitely wouldn't pay it off. If this is not the case, and you hate debt like I do, you could always just put some small % of your savings towards paying off the debt, and put the bulk into the market.