Should I pay off my low-interest rate mortgage or should I pay the minimum P&I and invest the money?
This hits on a topic that I consider to be as much personal as it is financial.
Financially speaking, a low-rate, long-term mortgage can provide you an inflation-hedge that simply isn't available elsewhere. It can provide you a significant opportunity to save and invest in other assets, while allowing you to gain in the appreciation of your home.
The key to that is a long-term view, and that you are disciplined enough to invest the difference in an overall plan that earns an after-tax rate of return above the tax impact of your mortgage interest.