Our county is in the later stages of this same type of deal, except they didn't hire an outside company to perform the task; they hired extra bodies outright and 'trained them up in the way that they should go'. The guy who knocked on our door was extremely polite and pleasant and wasn't the least bit pushy or obstinate. He was credentialed and had magnetic signage on his car identifying him as County Assessor's office. And he understood fully when I didn't let him in.

OTOH, just heard this weekend that a neighbor had a young kid (19-20) show up at his door with no credentials, no signage, nothing, claimed to be from the Assessor's office and asked to see the inside of the house. I never heard for sure whether he was let in or not, but I would certainly be uneasy about that scenario. That was my concern from the beginning of this, that it was only a cover for some unscrupulous people to case houses for later visits. 

Personally, I think it's a complete invasion, unnecessary, and waste of taxpayer funding. Especially in your situation, where they're spending nearly half a million dollars to do it. Wonder how long they project the increased tax revenue will take to cover the cost of the project? Would have been interesting to have heard the conversations at the supervisors' meetings.