All of this depends on your current financial situation and what stage of life you're in.
I have a 30 yr fixed at 2.65% after we renovated the house and put $400k into it. I could make $500-750k if I put it on the market today in a matter of 48 hours depending on the bidding war that would go on given our current housing market. This is not our final home as our family is growing.
In my situation, it is better for me to pay the low rate as is and take all "MY MONEY" leftover filling up 401ks, IRAs, kids' 529s, HSA and S&P 500 stocks. Reinvest the dividends for the stock, as well as the stock my kids have. The borrowed money doesn't matter to me as long as the note is paid. Investments will outpace and set us up for better retirement. My wife and I are both 38, good health and I have no intention of betting against myself.
To each their own. Consult with a Fiduciary, get a good accountant, work hard and give thanks to God. You'll be ok.