After these tenants move out, I'm thinking of just keeping the rental empty with furniture. It sounds stupid to give up $4,200 a month, but I really hate dealing with the homeowner association, move-in/move-out rules, and maintenance issues. Given that the condo doesn't have a mortgage and I have to pay taxes on some of the rental income, I'm not giving up that much. The condo can be a place for my sister, parents, or in-laws to crash when they want to stay in SF for longer than a week or two.
If you’re familiar with the phrase “don’t put all your eggs in one basket,” you know that it applies to just about any area of your life including—and especially—your finances. In addition to retirement becoming an ever-elusive goal, no one has guaranteed job security so by diversifying your income you can feel more secure about saving for your future. You’ll be less likely to find yourself in credit card debt and happier as a result of being financially secure.

Residual income is the amount of net income generated in excess of the minimum rate of return. Residual income concepts have been used in a number of contexts, including as a measurement of internal corporate performance whereby a company's management team evaluates the return generated relative to the company's minimum required return. Alternatively, in personal finance, residual income is the level of income that an individual has after the deduction of all personal debts and expenses have been paid.