My dad graduated from college at 48 (a few years after I did). He never used his degree, but, to him, it was worth it to have one. Both his daughters graduated from college, and he wanted to show that he could do it too. Financially, not a great decision, but the level of personal satisfaction was priceless to him.
My husband was in your shoes - late 30s, making $30k a year. He had been an auto mechanic for 15 years, and it was starting to take a physical toll.
We ran a lot of numbers for various scenarios, to see how our retirement date would change depending on what kind of job he was able to get, and with the decrease in savings while he was in school. Using my most conservative estimates, we'd retire 8 months earlier if he had a degree. Plus he wouldn't be further killing his body. He also looked at jobs like home inspector or insurance appraiser. He chose to go back to school for a technical IT degree - think networking, database administrator, etc. He loves tinkering with computers and had already built his own Linux server, so this made sense.
He first got an associate's degree from the community college. It was CHEAP. When he graduated with that, we ran the numbers again to see the financial impact of getting a new IT job at that point versus continuing on. He wanted to finish what he started, so he transferred to a university (NOT cheap).
We made the decision for him to quit work and go to school full time so that he could finish faster. He didn't work for 3 years, but he is working part time right now, in an internship that pays almost the same hourly salary he had before (and still going to school full time). For us, him not working hasn't been too big a financial hit - we were already living on less than my salary, and it eliminated day care expenses (he structured his schedule to be home when the younger kids got out of school), moved us into a lower tax bracket, and decreased some of our other spending (work lunches out, tolls, gas). The good news for him is that he'll be done with school at 40...and we fully intend to be retired by 49.
You live in Austin, so if you get a degree you'll be competing with young UT and A&M grads. Look for a school that has a decent career services group and can help you find either an internship or a full-time position. I know too many people who went back to school later in life and couldn't find a job in their new field - it IS harder for nontraditional students. Alternatively, be really good at networking (my husband's internship is at my company).
Good luck!