During ownership, these tend to be more expensive to operate relative to other real estate and lastly, for the limited few who can weather the storm and can effectively operate these properties, there is still a need for refinances.

What matters more is whether the borrower in question has the (i) time, (ii) contacts, (iii) experience, and (iv) ability to effectively communicate & package their loan request to banks & credit unions in a way that is compelling to those lenders. 

I was mainly thinking about the effects of putting an entire strong cashflow back into the mortgage.

How do I design a small yet effective real estate portfolio?

You will have to do something unique to make it effective & useful to you... because it's always no pain, no gain!

It binds the landlord, but honestly has little binding effect on a tenant when they simply choose to leave.

It seems like a more cost effective way to have multiple tenants. 

You have to keep in mind that a plex will never be valued the same as an SFH, and renovations may not have the same effect on the value as an SFH.If renovations are not needed right now, I would work toward getting the rent to market for the as-is condition and then renovate each side when you have turnover. 

Quote from @Sheraz Zia: Hi everyone,I’m managing the digital marketing for a real estate business, and I’m exploring PPC ads to generate leads more effectively.

Flipping can be cost-effective due to lower entry costs and growth in neighborhoods.