What normally happens in a 'domestic violence' 911 call: the police will go to the property, assess the situation, and over 90% of the time they will ARREST SOMEONE.

I've even learned how to search the public assessment and taxation sites to get further info on the homeowners I intend to contact.

Go to Tax Assessors office and have them update their records and get a copy of Assessment record.

I doubt it makes any difference in the assessed value of the home, for equity / financing, but it does make the home more desirable to tenants and buyers especially IF you are in a B market or above, and it is done tastefully (no tiger stripes). 

I am looking for a simple app (or even a different idea) for assessing properties.

You can also contact a property manager to get their assessment as to rental demand and rental rate.

Not an attorney or CPA, and I think you should consult one, but depending on what kind of upgrades were made, for you to get tax relief it would have to have  significantly increased the assessed value of the property.

but, have a contractor and/or home inspector assess how much damage they have already done.

I have arranged meetings with some groups/investors, my next step (so I’m told) is to compose a comprehensive RFP to present and review when we meet.

@Craig Bellot I’ve been crunching the numbers for a while and was having a real hard time making the deal close to cash flow positive, then I realized I was using the appraised value instead of the assessed value to evaluate the taxes.