I think you’re a little old to start speculating with money destined for retirement in a few years. Sorry for that brutal honesty, but there’s an old Savage Truth that says: “Desperate money never makes money!” You can’t afford to lose any of this money!
Since you’re still working you might qualify to refinance your home at a lower rate, on a shorter term — perhaps 15 years. If you can get your mortgage paid down sooner, you might use your home for a reverse mortgage when you are deep into retirement. And you might add some of your “extra cash” to pay down a bit of the principal.
BUT, don’t tie it all up. Leave some safely in a money market deposit account for emergencies. Surely you can discipline yourself not to touch it for anything less than a dire emergency!