We could always kick out an underperforming team
That might do more good than adding another team, IMO. But it won't happen.
What mid-major program(s) would significantly improve the MVC and would want to join?
There would be no shortage of schools who would apply, but it would look like a list of Summit, Horizon, & OVC conference schools. There are a couple that might be OK, but I don't see any that would be great additions.
In the last 12 years, the MVC has added Loyola, Valparaiso, UIC, Belmont, and Murray State. After a few years of mediocrity, Loyola turned out good for the MVC. Belmont is a good choice for most sports, and is a terrific basketball program, even if they draw far less than 2,000 attendance. Murray State is OK, but the jury is still out on UIC.
And Valpo has been a major disappointment. I can't blame the MVC for trying with Valpo. They dominated the Horizon for many years before they switched. And the MVC felt like they needed to replace Loyola with a Chicago area school in 2017.
But, check their records -
https://www.sports-reference.com/cbb/schools/valparaiso/men/
This is their 8th season in the MVC, and they have never had a winning conference record, and have played on Thursday in all 8 years in the tournament.
I hope things are on the upswing under Roger Powell, but, the MVC can't afford to add another perpetual loser.