If it's a brightness issue, try a small bit of electrical tape - cover the clock. BOOM! instant free dimmer.
Sorry, not trying to be an @ss, just saying, if you want to reduce electrical load to reduce drag via the alternator, cool - but the radio (depending on your setup) is pretty minimal. Still, I'm always in favor of modifying stuff. Did you run a switch, so you can turn it on while parked if the "need" ever arises? If you have a wire, you're one more wire, and a toggle away from switchy goodness.