How Should I Have Spent my Tax Refund?

I filed my tax return at the beginning of February 2018 and received a refund of nearly $10,000.

My 2018 refund was the result, in part, of my transition from the law firm to my current job in the middle of the year. The law firm withheld the maximum amount of certain taxes (e.g., social security tax) from my pay prior to the departure from the firm. However, my new employer did not take my prior employer's withholding into account. This means that too much of my pay was withheld and I had to wait for that pay to come back to me in the form of a tax refund.

In the interim between filing my taxes and receiving my refund, I fantasized about spending the sum on a trip to Europe, a new wardrobe, or updated furniture for the house. (Do not get me started about my family room couch--a now too small white couch that I originally purchased in 16 years ago.)

Instead, when my refund hit my bank account, I used it to make a mortgage principal payment that will save me up to $17,667.51 in interest expenses over the life of the loan and shorten the term of the loan by up to 13 months. Here are some reasons that I wanted to pay down my mortgage:

1. In the near term, I may recast my mortgage. As nerdwallet explains here, a recast is a reamortization of a mortgage that results in reduced interest expense without lengthening the term of the loan. Why would I do such a thing? I'd consider it if I were to move out of my home and convert it into a rental because the recast would allow me to maximize cash flow from the property by reducing my monthly mortgage payment.* (Currently, my bank does not require a minimum lump sum principal payment to recast or I probably would have invested my refund elsewhere in the interim.)
2. Regardless of whether I convert my home into a rental, I've decided to pay off my mortgage by a certain age. Especially as an unmarried person, I worry about a future disability that might keep me from working and, by extension, paying my mortgage. Even if such a disability never comes to pass, owning my house outright will give me more flexibility (to work fewer hours or a different, more "fun" job) as I age. When I reach retirement age, I may be very alone in this world with no one to lean on but myself.
3. I couldn't come up with a better use for my refund that would be accretive to my net worth. I don't have debts other than my mortgage. My emergency fund is fully funded. I have plenty of investments in the market (and continue to be bearish on equities), which are constrained by my employer's compliance policies.

It turns out that my mortgage principal payment may have been a not-so-good idea. About a month after I made my principal payment, Financial Samurai posted this article about why it's a bad idea to pay off a mortgage when the yield curve is inverted. How do you think I should have spent my tax refund?

*You may raise an eyebrow given the historically low interest rates offered by banks over the last several years. While it's important to remember that my mortgage amounts to a "cheap" loan due to a low interest rate, I'm primarily aiming to get the aggregate amount of my mortgage payment, property tax and homeowner's insurance below the prevailing rental rate for homes similar to mine.