Ha. I jumped in because your subject line said "prepay mortgage?" and was about to rip into that, but you've already fixed it. Love the caller comment too.
To answer your question, there's no wrong answer. Would you prefer the "math" option of investing or the increased security of lowering your cash flow needs? What would the person who bequeathed you the money feel about your choice? Does that really even matter to you? Max out those tax-advantaged accounts first either way.
After funding investments, our household budget is near equilibrium. Thinking that nixing the mortgage would give us some additional breathing room while letting us increase some contributions to taxable accounts.
I don't get how this is a problem. That's how it's supposed to work. Spend on your needs (and wants) and invest the rest. If you're feeling squeezed, then back off on investments. You've done well though so I'm a bit skeptical that you
need to spend more. If you're paying off your mortgage just so you can upgrade your lifestyle, you're missing the point of this site.