re: First Mortgage Question - 15yr vs 30yr vs. Investing "Extra Payments"

There are two major factors you're forgetting:

1) With a mortgage you're probably going to be able to itemize deductions. This means your interest payments reduce your tax burden, which means your true interest rate could be substantially lower than you think.

This shrinks the difference between the 15 and 30 year options.

2) Long term rate of inflation is (typically) around 2% or so. So it is a mistake to focus on monthly payment amounts alone because $1000/month in year 30 isn't nearly as valuable as $1000/month today.