If that was the case here, the current balance could be quite a bit higher than the initial balance. 

My retirement system doesn't allow for me to roll anything over given that I'm still employed with the company and also under 59.5 years old.

@Tristan Kelly hope this goes well for you!

Vanguard and Blackstone have a lot of interest here as well. 

We have found what works and repeat it as much as funds allow.

I feel like there’s a balance between being decisive and being reckless, and I’d love to hear how you guys approach this.

The 5% of the remaining balance late payment fee is a little much IMO. 

I'll be getting several more opinions from other plumbers as well.  

Paying off the mortgage can provide peace of mind and simplify retirement, while keeping the debt allows you to leverage your funds for higher returns through investments.

Austria, Germany, Luxembourg; these immediately come to mind as "ancient" developed areas in contrast to the "infant" that is USA, and they seem to be doing very well, very efficient, very well setup and established across the strata's.