The first question is if you can see yourself doing this current job for a long time.
The next question is where your pay is in relation to the pay range. Would getting more education allow you to do more of what you enjoy and still be paid well for it? Or would it allow you the option to switch careers, just in case? Additional work for min. wage probably isn't worth it unless you can't pick up additional hours in your primary job which may translate to promotion or higher rate.
I'd use the excess time to develop some side business.