Hoi,
Return on investment is in our context all too arbitrary. Ask yourself; is investing in gender gap important but does it make the best return on investment. At the time I invested in documenting every person who died in Wikidata. It was a good investment because now people have taken over from me. Now at years end they use Wikidata to know who the "famous" people are.
The question is not bang for the buck. The question is where are we weak and how can we change this. My current project is adding information about the nobility, the monarchs of particularly Asia. I am learning as I am doing this and I blog about it. All the investments in students working on Wikipedia does not make the quality of the subjects I write about better. Many of the stuff I am involved with has a point of view that I find is hardly neutral. It is however not the subjects students are taught.
When a chapter, a community finds that a specific area is important to them, they should be able to do so. Their relevance and work / investment is not to be mistaken for a provable "return on investment". Because of the gender gap I do give more time to the women I find. That awareness is something you cannot measure but it does have a bearing. People with proper historic knowledge could do much more; they would study the relationship between marriages and peace between countries when they are ruled by monarchs. They would bring this out. At this time we do not even have many of the important battles and wars from the past... I am not saying this is more important but it paints the picture.
When you want return on investment, there are the things people do not care about because it means that it changes the way things are. The best return on investment for Wikidata is by replacing red links and wiki links with references to Wikidata items. I dare anyone to find an argument how it will not bring more quality to any Wikipedia.
My point is that we will only look into the things that we know and care for and in the process forget what we do it for. Money / investment is more of the same. I prefer that we trust more and do not measure using our own yard stick.
NB I am into meters and metric myself :)
Thanks,
GerardM