We'll likely throw money at it once someone moves out and we need to improve it to increase rents yet again. 

Since they have been really good renters and have at times been some home improvements themselves without asking me to reimburse,  what would be considered a reasonable and fair thing to do?

There are definitely homes under 140k and would rent really well, especially older homes in their improving downtown. 

After all that, make sure your rental rates are SOLID and you are accounting for maintenance, management, and vacancy in addition to your other fixed costs (taxes, insurance and mortgage).You can find more info on my link, on my youtube or facebook if you want any more help on this. 

I have watch tons of videos on youtube i am currently living in new york city where housing market is really expensive .

On the other hand, investors often are the only ones putting money into renovating these properties which gradually improves neighborhoods over time.

Equity comes from improving the property, raising the rents, i.e., making it worth more than when you bought it.

and or check for little improvement that might help you increase a bit the rent. like $10-$35 extra.

Make small improvements to the home that we are currently in so that we can rent it out.

Facebook, Facebook marketplace, YouTube, Twitter, Instagram, etc.Leasing Team.