If a renter can (mostly) pay off the mortgage... talk about your house getting a job. While its true that the value of a house is what the market will pay for it (and by that definition, you may be underwater). There is much value in the house bringing you a passive income. I would go ahead and buy a second home, fix it up and make it your own and then... become landlords. Get both properties paid off over time (you say you'll be able to purchase the second property for cash so put extra money towards the mortgage of property 1). Once this is done, the rental income you earn can be used towards the purchase of property number 3, and so on and so on.
I agree with you that foreclosure is only something you thought about briefly... it would be stupid to throw away all the mortgage payments you've made for several years when a renter could be paying you to live there. Forget about what the house is worth on paper and care more about the monthly deposits into your bank account. If the housing market went down since you bought the place, it will eventually go up again...
Good luck!