What is a good tenant worth?

[Pat Jackson]

I looked a duplex about a month ago, and have been meaning to ask this question since.  This is an up/down duplex.  Each unit is 3 bedroom, 1 bathroom.  Already 100% rented.

The top unit rents for $575, could probably be raised to $600.  Nothing really not note, it was a nice unit.  The downstairs is nicer, and has a very long term tenant, he pays $465.  His unit is certainly worth $600 a month.  Let's say I'm wrong though, and it's only worth $575.  That's $110 less or "loss".  Before one screams raise the rent, here me out....

1.  He's been there for 5+ years and doesn't want to leave.  He's probably 60, and pending some catastrophic event, from what I can tell he wants to stay there till he dies.

2.  He mows the yard with his own mower, which is a value of $500-$550 a year.

3.  He takes immaculate care of the place, he tends a nice garden, planted rose bushes, a peach tree, all sorts of stuff.  This house is in a C neighborhood, and it has the nicest yard on the street because of his efforts.

4.  He loves the place and was there the entire time I saw his unit, talking about the whole thing.  Really proud of his home.

5.  On #4, he is a bit of a character.  Type of guy that will talk your ear off.  I'd have a property manager so it's not a huge deal to me, but just fyi.

So if I bought this, and lost $1320 in rent, got $500 back in value from lawn care, we're now talking $820.  So what's a good tenant worth?  Raise the rent to $575-600 (he'd likely leave as he's on partial housing assistance), raise partway and hope he stays, or leave as is and have a "good tenant"?