While it was tempting over the years to refinance for a variety of reasons -- we didn't. The interest rate slowly declined until it actually hit a floor of 5.125% a few years ago when interest rates were in the low 3% range. But by that time the payments were mostly principal reduction, so refinancing didn't make much sense.
And now, here we are, 30 years later, with one payment left! Never thought I would see the day!