Hi Scott -
As you've been told - there is no substitute for boots on the ground property analysis. All of these auto generated value estimates are ineffective as they do not take into account the myriad of physical, locational, condition, quality and functional utility differences inherent in every home - there are no two identical homes. Another huge variable is square footage; what actually constitutes it and how to calculate it - see this article:
To add insult to an already injured market, the appraisal business is steadily moving toward Automated Valuation Models (AVMs). The result is a diminished level of appraiser input - it started years ago and every year it advances more and more. More reliance is being placed on the values spit out and when there is an issue a warm body appraiser is brought in.
If a very reliable estimate of value is desired, call a certified appraiser. Remember though, appraised value may not be market value. The ultimate authority on value is what the ready, willing and well educated buyer decides to pay for it.
There's a good article on my site You're in my backyard, shoot me an email if you'd like the name of an appraiser or a detailed opinion of value that I can easily prepare.
Hank Miller, SRA, ABR
Associate Broker & Certified Appraiser
REMAX Greater Atlanta