I used to do this all the time as an investment real estate accountant.
It's called a hurdle number, and it's easy to calculate. You have some number in mind that you think you should be able to make on an investment. Right now, most smart finance people are assuming around 4% a year. So you have a Kingdom Hall that should sell for say, $200,000. If you sell it and invest the cash you would expect to make $8000 a year. Do the congregations occupying that hall send you more or less than $8000 a year? If less, you sell and invest the money. If more, you keep it.
I bet somebody, somewhere as performed that calculation for every piece of property they have. The only remaining question is how quickly they'll dump the losers.