Hi Byron,
Have been pondering this whilst on a mega garage clear up this weekend!
To give a bit of context, I went to University full time at the age of 28 to do a degree in Environmental Sciences. After that I did a PhD and then worked as a research associate for a few years. My specialism was fluvial geomorphology (the study of the physical form of rivers), particularly the effects of climate change, as well as the restoration of habitat in degraded rivers. I also worked on a project simulating the movement of pollutants in estuaries under various sea-level-rise scenarios.
I now work as a software developer for a firm of civil engineers... :? :?
I have to say that my experience as an undergraduate was great, and my only regret is that I didn't do it sooner. I knew several mature students and I think they all felt the same way. I have also known several people who have taken OU courses and degrees, and I think they have all found it hard work, but tremendously rewarding. I was going to suggest that doing a short course to start with might be a good idea - I see you have already come to that decision.
You said you have many areas of interest - again, starting with the short course will give you more time to get a feel for where you might want to go. You might also find, as I did, that a broader degree will leave you with a wider range of possibilities for future careers. Bear in mind that to do research you will need to do a PhD anyway (I'm speaking specifically of the Environmental/geoscience areas here - it may be different in other fields), so doing a broader course to start with won't hold you back.
Steve's comments are also applicable to the Environmental field, I'm afraid. There are mature students I know of who have made it as far as lecturer, but they are few and far between. That said, the work can be very interesting and rewarding - it can also be quite mundane at times, often for long periods of time.
I have to say, that how the pros and cons balance out is a personal thing, and that I no longer work in scientific research is due more to getting married and becoming a Dad than anything else. Financial and job security became much more important than when I was single. The work itself, I always enjoyed.
There is a lot of work outside of academia. I don't think there is likely to be a massive demand for climate change specialists, and it is worth pointing out that much of the work to do with adaptation is the preserve of social rather than physical scientists.
I would agree with Greybeard here. Many people take a career break, do a course and then return back to their original career. They do their course for the challenge, the interest and sense of achievement. It doesn't have to be seen as a road to something else, although if it turns out to be, so be it!
Ask away if you have any questions about the environmental side of things. Hope I haven't waffled on too much.
Dave