There is a valuation process, it's that in residential deals it's too much brain damage, not that it's impossible to do, so 10% is viewed as a relevant option price, but it can be less, as to consideration, establishing an equitable interest and over a reasonable period of time, 3 to 5 years usually.

Didn't really think it would be worth the brain damage of paying the bill and collecting the money from the tenant but perhaps for large users it might be.

Essentially, I am saying it's a bunch of brain damage to have a "potential" value which frankly might not be so accurate based on time.

I also charge my tenants a $50 service call for repairs that as long as its not due to tenant damage gets refunded to them so I don't think I would have much of an issue with regards to unnecessary repair requests. 

If a dog damages the property or disturbs other tenants they should be financially responsible just like someone would have to install and then later remove their own grabs bars or accessible fixtures at their own cost (at least in CT).

In a very bad scenario, the structure is damaged, the land value is reduced (I heard that happened after one of the previous earthquakes here before) and there is still a mortgage payment every month with no rental income.

If you don't insulate the pipes for the tenant unit and there is a break and/or damage, it's not like you can charge the tenant for repairs.  

We got enough to rebuild the damage, and then sold the house.  

We hired a painter at our last turnover as they were there 2 years and it already needed a full paint job, so he listed the hole in the wall he had to repair and the excessive damage to certain rooms and split the bill accordingly, then charged the tenant's deposit for their part.  

You may want to look at getting them out of there before any crazy action against them, I can see them doing a bit of damage if they knew you were going to take them to court.