I hope you get a dimmer It's worth it. I plan to keep them dimmer going even after I get a nice thermostat. I don't want to lose any snakes because of my temps sky rocketing! I'd rather everything shut off, they can live just fine in 70 degrees!
Just to clarify: Dimmers don't cut off your power. They limit it so you can set a max temp in case the thermostat fails in On mode. Your thermostat appears to have failed in Off mode, so your dimmer didn't do anything.