You have A LOT of equity on this property. Some investor will frown upon it saying you should take it out and use it to buy more properties. Other will cherish because it means less risk and more cashflow.
Some things to consider:
1. As Mr. Rolf said, you can sell tax free since you've lived there and pull out the equity, but if you don't you can also do a cash out refinance at any point in time and pull out tax free money from it as well!
2. If you sell, your closing costs will be about 9% of the sales price and when you but another property with the money you will have closing costs again of about 3% of the purchase price.
3. $700k properties are on the high end of the spectrum for rentals. During a recession, these are usually the hardest ones to rent out. However, since you owe very little you should have plenty of room to lower rents if needed.
4. Houston is growing very very fast. It has very good appreciation. There is a chance it the appreciation alone will outperform anything you buy on another city.