My interest is strongly piqued!

The ROI resembles that of physical exercise: annoying time investment into something that is unwise to ignore on the long term.

With exercise I can see how this works through several layers of inference. Exercise leads to more efficient slow or fast twitch skeletal muscles, a more robust cardio vascular system, more flexible joints, stronger bones, and so on. Being fit makes it easier to exercise and stay fit, and one can see how different kinds of "exercise" fitness would logically connect to issues like broken hips and heart attacks that are the proximate causes of death and disability. Some people can ski in their 80's but most people are dead by that age. The whole conceptual package of exercise is also backed by medical studies that regularly show substantial health benefits to a physically active lifestyle.

With meditation I recall studies connecting it to some "mental health" improvements, but I'm at a loss to fill in the mechanistic details... I'm not sure what scary outcomes I'd be avoiding, what the proximate causes of those outcomes would be, how "different aspects of my mental machinery" could be tuned up as preventatives, or what specific "exercises" to do. I'd heard that cross word puzzles might help with senile dementia, but when I looked up the research just now, the most recent results actually suggest that cross words may delay the onset of dementia but speed the decline after onset. Is meditation like cross word puzzles or is it better... or worse?

Or for that matter, maybe you're not talking about brain physiology. Maybe you're talking about mindfulness and the way it can help people avoid making mistakes in life (though I've never heard good evidence for that).

I did hundreds of hours of meditation, mostly Vipassana.

Given your hours of practice, and the expertise that implies, and your comment about long term outcomes, if you can sketch out any information I would totally appreciate it. I bought some juggling balls after the juggling study came out, and based on sporadic practice I'm up to trying to master mill's mess, but a lot of that is that it just turned out to be fun (which I don't expect meditation to be).

I think if I had concrete "inside view" motivations to work on meditation, I'd be much more likely to give it some time. If you could help with this, you'd have my thanks :-)