Their tax base is deteriorating and so the prop taxes as a percentage of value are often wayyyy out of whack.

For the remaining windows, in less-conspicuous locations, I am considering installing new double hung wooden windows matching the style and compatible with the dimensions of the originals, for example: https://www.homedepot.com/p/JELD-WEN-33-375-in-x-4....Doors - The front exterior doors are deteriorated and the security doors do not match.

The husband had passed away and the wife bought a new house and the beach house had sat for five years and started to deteriorate. 

Depending on how title is vested now, it may require pronating Decedent's estate2) Back taxes will need to be paid within time frame mentioned3) Substantial improvement budget required4) Pending winter weather means further deterioration and possible damage5) Winter is harder to repair exterior and sell.

Also, the weather "anywhere that is not SoCal"  adds an element of "more rapid exterior deterioration" that is of course not seen in SoCal, and this must be budgeted for. 

Depends on location, too.I've got properties in low-income 'transitional' neighborhoods where various slumlords have let their properties deteriorate badly.

That's $900 per year in reduced rent.The cost of the additional renovations should be about $5000:- Cabinets: $2000- Countertops: $1000- Bathroom Sheetrock: $500- New Toilet, Vanity, Faucet: $1000- New Tile Floor: $500The other stuff we'd have to do anyway, including kitchen floor (which is in really bad shape), tub surround (deteriorated and water getting behind it, causing mold), shower door (it's destroyed), etc.So, a $900 annual return on an initial $5000 investment ends up being an 18% cash-on-cash return.

Also a concern that a non-performing buyer will allow the house to deteriorate.

I've seen many a landlord pour money into improvements and then see their investment deteriorate when they allow D class tenants possession.

What's that, commercial policies don't cover damage caused by sewer drain lines deteriorating to the point of leaking sewage down into the kitchens below?