Coming from someone who has a crummy job and who is actively looking for work in this crummy economy, I have to be honest when I say my personal opinion is that you should stay put and focus on the positive things your work affords you. Is there any way you can make your work life more exciting just by changing your attitude?
Your job sounds like something I would love to have.
If you went back to school and quit this job, you would be having just as much trouble as your husband finding work somewhere else - and there's no guarantee that you would like that work any better, or the people there for that matter, any better.
So if you quit this cushy job, you're taking a huge gamble on many different things. You're taking a gamble on finding work elsewhere in a reasonable amount of time, you're taking a gamble on whether or not you'll actually like that work for another 20 years, you're taking a gamble on the types of people you would be working with at the new job, and you're taking a gamble on whether or not more education would pay off in the long run.
You really need to think about this long and hard. More education doesn't necessarily guarantee anything except spending more money on it. That's just my personal opinion.

I would definitely stay put if I were you, and I would try to make work more enjoyable. I wouldn't take this huge risk while my husband is struggling with permanent employment. Personally, I would be afraid that I would end up hating the new job and not liking the people I work with in a new job. You might not be able to imagine doing the work you're doing now for another 20 years, but what if you took the chance and got a new job and you couldn't imagine doing that work for another 20 years either? My sister said to me the other day, "No one likes their job! You just have to do it! Stop trying to look for the perfect job because it's not realistic. Everyone doesn't like going to work, that's why its called work." She's actually right.