If you want the work to be quality, then there are better actual small single-man operations that are cost effective, but a bit more $.

I would be inclined to keep renting to them, but have several inspections per year to make sure things are getting worse and try to get them to clean up their act some and address the extra cat.You could make it a requirement that they clean up their mess (or at least organize it) before you will renew their lease.

it could effect your banking relationships.

it is quite a process and generally not cost effective-there are services that will sub meter for you for a fee but in that small a complex it usually does not make sense.

Most cost effective would be ideal.  

The "HGTV Effect" is certainly real.

This also has the effect of slowly improving your tenant pool by adding people with more disposable income. 

Keep in mind you will have cleaning fees in your expense column, but those should also be included in your income column in addition to your nightly rate. 

The interest charge is negligible 4.75 and it is tax deductible, for a net effect of 3.5% (assuming 33% tax).  

I'm curious to know if anyone has had luck with virtually staging their properties.  The thought is that the potential buyer can walk through the property with the listing pulled up on their phone and have an example ...