You have to think about this...In a year or two or more when the housing crisis is over (it will end just like it has every other time it has happened since the beginning of time) that your equity may be doubled and that would be the time to invest.
Another look...stocks are down, housing prices are down. If you weren't so strapped, I would look for a fixer-upper in a great neighborhood to fix up over the next year or two and, hopefully, when that house is finished you'll have sweat equity as well as rising housing prices to make a sweet buck.
Now, considering the fact that your strapped, to many unpredictable things are going on right now. And it would be a real shame to be all stretched out and have a crisis and have to let go one of the properties.
Im a gambler and we have about 80 in equity and we're stting tight. Im also a real estate agent and I can tell you good deals are plentiful right now but they still happen in a good market. You will need to get serious when the time is right and have a good agent who will do searches for you every other day or so to keep you posted!
Good Luck and feel very fortunate you are sittin so pretty right now. I know it doesn't seem like it (I know because my hubby is an electrician and I ain't sellin poop

but all your hard work will prevail.