Your gut will tell you what you are comfortable with, appreciation plays, high crime areas, jobs in the area and your tenant’s earnings...risk related stuff, mostly out of your control.Numbers or cashflow, go pick up Frank Galinelli’s book.Market, are you reasonable for the area, does your property command more or less than comparables, is this even the right market for your goals?.

Let's further suppose that $4k could be used to upgrade the kitchen, which would let it command $75/mo in additional rent.

Many senior parks are very well kept and do command higher lot rents.

I see really dated places for rent but they are sf and it makes sense to wait to renovate if you plan to sell later, even if rent commanded is less.

Their command forced their hand and issues went away quickly. 

AS your growing your portfolios I see this austerity plan working.. but I would say the biggest driver of young families is school districts at least were we live  its not like the deep south were far more kids go to private academy's .. so school districts will command much higher prices if they score well. . 

But yes, window units will definitely command lower rents. 

And if they are late on rent or trash the place you can call his or her unit command.

One of the REI commandments: Thou shall not buy in a market with persistently declining population.

And yes, I know of multiple friends who live in apartments here in the city  that have not been renovated for well over 25 years and they still command $2k/room.