Damn, where are you that you're only playing $825 in rent but the cheapest house you could find would be $500k? Or do you have roommates? Definitely sounds like a renters' market.
Obviously there are so many little things that affect those estimators. Lower your purchase price to $400k, increase appreciation to 4%, and stay in the house 10 years and it will be an entirely different picture.
If you're comfortable where you're at, then definitely seems to be no reason to change course. Plus, that'll give you more flexibility down the road if you choose to move, start a family, etc and you'll be sitting on a much larger pile of cash to buy a place then. Beware cost of living creep however, if over time you move to a $1,000/month apartment, then decide you want a swankier place and move on to a $1,500/month even though you can 'afford it,' you could quickly erase your current financial advantage of renting.