If you don't plan to sell,buy or refinance your home, Zillow does not do you any harm. If you do plan to do one of those things then it is better to check with a professional real estate or loan agent for a CMA. Only the most recent comps can tell you how much your home is worth. Market is very dynamic and unfortunately your neighbors' financial situation does directly affect your home value.
Website like Zillow only gives you general idea, if a house needs lot of updates then it will be sold below market value because new owner has to put $$ to improve it.