@Dave Fagundes
"So the big question is: Does the rise of the mid-rise in the Inner Loop spell decline for the market in rentals of units in smaller multi-family? Or are there other factors that cut back against this trend? Thanks for any thoughts on this."
Short answer, No.
Mid to high rises are a different class of properties compared to small older multi families. Classes D to B- in the small units because of age, condition, and location. While the mid to high rises are class B to A. Different demographics as @Kyle Bryant stated.
Gentrification can also plays a role in these small milt-family properties.
Vacancy rate can vary because of quality, management issues, hurricane, economical turn down, high crime, bad schools, etc...
So, I would look for class D to C- property in a solid class C+ to B area and not worry about the mid to high-rises. I would look at that as opportunity especially because of the type of property you are looking to buy.
My apartment, for example, was a class D- property in a class B area. After a complete renovation and turnover, it's a class C+/B- property and, we are above market in rents per S/F while maintaining high occupancy. In Katy there has been a huge influx of new apartments over the years, to the point of being overbuilt. however, we are still maintaining a high occupancy rate because of the class differences.