You have to consider that cost, and getting a new, unknown entity in your building, who may move in a year, and cost you a month's rent again.  

If it's a wash, or an unknown gamble, then you are wasting your time to do any more to the property.It's a tough decision only you can answer but right now it's costing you more money to hold. 

For an unknown reason my dog decided to try and rape the guy.

Filed Unlawful Detainer on all and 'Unknown Persons'. 

I bet you'll spend a lot more than that getting that unit ready for a new tenant - who is an unknown. 

It may put a huge financial strain on the owner to try to cover the principal payments on two properties in order to get appreciation at some unknown future date.

I check for mail and any names where mail is getting sent to your rental unknown to you.

I think that's too long to wait to recoup that money, and for an unknown.  

These unknowns can be dealt with in the lease with a clause about letting the new tenant break the lease if the unit is not ready on time, but it will still be a pain.The best way to get a tenant to be cooperative for showings, is to pay them. 

And you won't have the unknown future cost of rising dues.