Education is critical in both keeping you sharp and paving a future for yourself. You will always find the old salts, sitting somewhere, weathered skin, callused hands, aged beyond their years, maybe a General contractor, maybe an NCO, espousing the benefits of experience over education. It is true that with some hard work and a little luck you can make a decent living without an education, very true and if you are after a craft, or a trade experience and "know how" are everything.
But
With an education and similar experience instead of being out there in the ditch, or on the roof you are in a trailer or an office downtown making certain everything runs properly. Same general field, but instead of being out there taking years off your life you're checking your email, making dinner plans, and still getting more done with a pen or a phone call than anyone at three or four job sites.
Education opens doors that otherwise aren't even visible. In most cases an education has nothing to do with intelligence either, I know lot's of idiots with masters degrees and I know lots of blue collar types that should or could be holding PhDs. Never stop learning, whether you are simply watching education television instead of freaking American idol, reading a book, or taking classes at the local U just cause you want to...
Education is something that will always pay off, always, even if it doesn't pay HUGE CASH dividends, it will still keep you mentally sharp.
If you think the education you already have isn't working out? Then absolutely go back to school and find something you love to do.
Besides, if nothing else, the jobs a good education will get you pay much better, with better working conditions, better benefits, and usually reduced physical wear and tear...