I'm a little loath to reply to this on the basis that the vast majority of posts from the Slashdot crowd on anything to do with university tend to view education as all about money. I suspect that's a heavy cultural bias from the US... anyway.
As someone who is a 40-something about to finish a degree this year, I have some experience of this but for me, at least, your question loads the dice. I was earning plenty of money doing what I was doing before, I just didn't like it. I'd be happy to earn a living, doing something I love and that is what, in my experience, most mature students are doing back at university.
Granted that might be a little skewed because useless public services like healthcare and universities cost more in the US than anywhere else in the world, and maybe you do feel some pressure to get a career result to pay back the debt. That said, there are cheap or even free ways to get educated if you're willing to move beyond the top-tier universities.
Finally, I'd add this: It's easy to make the decision to go to university to study something based on some sort of future goal. What universally happens is that by the end of the degree, you have a different idea about what that goal is. It's also quite hard to motivate yourself, do well, and even benefit particularly well from a degree if you aren't really interested in the subject.
So my advice is this: do a degree in something you're really interested in and when faced with choices, go for the flexible choices. There is every chance that you'll run into some niche off of something you're interested in which will turn out to be a gold mine. It happened to me. I found a field that blended my previous skills with what I was learning and it's the best thing that ever happened to me.