I should also add that I would for emotional reasons be happier paying down the mortgage faster, even it if meant losing out on stock market gains. There's something about a paid off house and not owing a dime to anyone that appeals to me, even if it's not rational to make decisions that way.
Yeah, not so much as you might think. You will always owe utilities of some sort and taxes. Always taxes. We paid cash for ours and it still kills both of us not to have a mortgage when rates are so low. We have over 1M in our stache, not including the house, so it's definitely a FWP. In all cases, I wouldn't prepay one red cent unless and until all available retirement account options are stuffed to the max.
This is why it's a personal decision. We did pay off our house at a low interest rate. Of course we still have to pay taxes and insurance, but coming up with $10,000 per year rather than $45,000 per year is a completely different issue. I liked the idea of knowing that if things fall apart, we'd have a place to live, no debts, and we could eat cheaply if we had to. That gives me the security to fully invest in the stock market knowing that I don't really need that money, and it turns a risk averse person into a risk neutral one.
Behavioral economics does matter. If paying down the house makes you feel better, do it, especially if you're also investing in the market through your retirement accounts along the way. (Do make sure you're investing in the market along the way!) Just be aware that the truly economically rational way to handle a low-interest mortgage over a long time period is to invest in the market at estimated 7% growth (with volatility, but less volatile over a long time horizon), rather than accelerate the mortgage payments.
Don't feel bad about no bi-weekly mortgage plan. All the advertisements I saw for them included recurring fees for giving you that option--it was basically a marketing ploy to increase revenue. The default seems to be that sending in a partial payment gives you no credit until a complete payment is received. So just send in however much extra you want with your regular payment, and you're good. Or if your bank makes it easy to do, send in additional payments designated principal-only just for fun at random times. Yes I just said that--it's a Mustachian forum.
Finally, if you haven't already, consider getting a home equity line of credit (HELOC) to use as a substitute for large cash reserves. See the MMM article on "Springy Debt." That's what actually got me going down the path of Mustachianism, and it really made sense to have a HELOC that you can tap at any point at a very low interest rate, which works pretty much the same as cash reserves in case of emergency. The only downside is seeing the confused look on the banker's face when you explain that you don't need the HELOC for anything at all--just in case of emergency!
Good luck, and hooray for the supportive wife!