IMO, Yes....yes it is worth it. Many years ago I worked 10-15 hours / week OT for months on end.....I saved up a nice chunk of change from that time. Another time I pulled a double shift for a week.....ka-CHING when that paycheck showed up, even after getting assaulted by the tax man.
Your marginal tax rate is going to be pretty low at those hourly wages, no matter what. OT may kick into a higher bracket - depends on your circumstances. Even if you kick into a higher tax bracket, unless you jump multiple brackets, you'll likely still make more per hour than at your base rate. Run the numbers using your last years tax return as a guide of what you might expect to happen.
Hypothetical Example where your OT is taxed at a higher rate (in the event your increase in income pushes you to a higher tax bracket - recall, however, that only your dollars above the threshold are taxed at the higher rate, NOT all your earnings, so your base wages will still be taxed at their normal rate):
$12 / hr x 15% tax rate = $1.80 hr / tax. Hourly wage after tax = 12 - 1.80 = 10.20 / hr.
$18 / hr x 25% tax rate = $4.50 hr / tax. Hourly wage after tax = 18 - 4.50 = 13.50 / hr
Google "IRS tax witholding table" and you'll find the info needed to figure out where the break points for higher brackets will be in your circumstances.
Just don't fall into the trap of spending extra because you're working OT. Pre-make your dinner and lunch so you don't have the excuse of "I'm too tired, so I'll get take out / go out for dinner just this one time....." It's easy to blow a significant fraction of the extra you're earning if you fall into these kinds of traps.