Check the foreclosures in your area. Foreclosures have really skewed comparables during the down real estate market. Your insurace company bases its coverage more than likely on the cost to replace it and not market value. If you are paying real estate taxes based on a higher worth, you need to talk to your assessors office and get the tax bill down. If you continue to hold it, the down real estate will return to normalcy in time but when is the big question. For a long term investment, you are in good shape.
Because of all the litigation resulting from fraud in the mortgage business, my person opinion apprasiors have become ultra conservation. I would get a very reputable appraisor who really knows your market to look at it again and I would ask him questions about the state of the market in your area.