I feel like you are approaching this from the wrong direction, a sort-of solution looking for a problem perspective.
So perhaps roll back a bit - what are you hoping to get out of these open source projects? What does the company hope to get out of them? (those are likely different.)
More generally, what does the company want out if this code?
only by determining the goals can one even understand how you might align them.
All software projects need love and attention to grow and change. But companies usually see software as a tool, not an ideallogy. We have lots of internal software that is 10 or 20 years old. It performs a task every day. It does the job it was designed to do. It gets zero attention, just like the toaster in the kitchen. We don't have someone fiddling with the toaster everyday either.
We have other libraries that are core, they are maintained all the time, docs are up to date, unit tests, and so on. Closed or open they get daily love.
But our company has no specific "open source goals". We don't care about github stars, we're not measuring downloads etc. We actively evaluate pull requests, and most get merged in.
So in short, I think you need to determine what the goals (direct an indirect) are for each project, and from there allocate (or not) resources to that project.
If there's no harm in open sourcing it, then great, do that. If you want external engagement (git hub stars, external contributers for free etc) then that's a somewhat different problem to the question you asked.