Wash-rinse-repeat.

This coverage is very cheap and can keep you solvent if you were depending on your asset's revenue to pay the mortgage.  

Or would this end up just being a wash against our primary residence?

You're not doing yourself any favors having that stained carpet in the house, I'm surprised your realtor didn't recommend replacing it off the bat.If that fence wasn't painted, you can have it pressure washed. 

They once offered up the basement for furniture storage for a charity drive... and also used the washing machine to wash about 20 loads of clothing they were going to donate. 

I say the same with garage door openers, wash machine too.

When she had company, she tore the paper plates in half and the napkins in half and washed the plastic forks for reuse.

Ultimately, it depends on the recovery rate of the water heater {gas or electric } and whether your washing machines are High Efficiency (HE) units.If you have 2 HE washers, then a 40-usg tank should be ample.  

Like saying I robbed the bank to pay for granny's operation.So, in reality, all these "iron glad" contracts devised by wholesalers is nothing but a leaky bucket, eye wash to get a seller to closing.   

My fourplex has a service that they service the washing machine/dryer and I collect a percentage based on the usage.