Home insulation - ACTUAL utility savings?

Rats means full suit and respirator level clean up. You might want to consider a specialist contractor for that work.
A proper job for that is remove insulation, rat shit, rats and whatever. Plug any holes, then spray shellac based sealer (Kilz or similar, another suit and respirator job) on the joists, install baffles at every vent, blow 12-14" of cellulose.

Look for a contractor safety store and get a proper respirator and suit if you DIY. Those dust masks at HD won't protect you from the bacteria and viruses those rats left you.

 

I had to find this post... here are some pics of our office job.

 

Heat rises. Go outside and look at your roof when there's frost on it. You'll see the weak spots if the frost isn't consistent.

 

Frost.....what's that?

 

Our old house was built in 1972 and was 1600 sq ft. We had new attic insulation blown in and replaced the AC and handler and our electric bill dropped about $40 per month. We probably would save more money if we put in new windows but we sold the property before we made that upgrade. Savings will vary because I have to have it at least 71 to sleep with a fan blowing (summer).