Residual income is the amount of personal income left after an individual has paid his bills and periodic mortgage payment (expressed on a monthly basis). Residual income is an important consideration for a lender; if a loan applicant shows a large amount of residual income remaining each month, this means the person's current income level is more likely to support the payments associated with an additional loan. Conversely, a minimal amount of residual income is likely to trigger an immediate rejection of a loan application. Residual income tends to increase dramatically later in life, after a person's mortgage has been paid off.
I agree mostly with the real estate advice. I’m looking for ways to take advantage of the condo I own to get up the rent from ~$0.90/ft to the $1.2-1.5/ft that seems more like the range in the same area. I’d have to put in a bit of capital (probably 10k on the low end for just the basics up to 40k if I wanted to remodel the kitchen and 2 bathrooms up to par with the area), so the return is likely there if those upgrades warrant $1.30/ft (given the unit is larger than most 2br/2ba in the area).