I'm an EE having working a significant part of my career in radar systems integration and test.. and a tight wad as well. On my personal aircraft I always keep the radar on. If your concerned about RF then ditch your cell phone, it right in your face so to speak. In the case of the WXR energy is very well focused and goes where the antenna is pointed vs up your tail pipe. Also the listen time to TX on time of a WXR is typical a 1000 to one. Transmit for a few of micro seconds at a few hundred watts, then listen for a few milliseconds, resulting in an average RF power of a few watts.
On the other side of the equation, two items that take a heavy toll on modern electronics are moisture and thermal cycling. Keeping the WXR on keeps it dry, and turning it on when cold soaked at altitude will cause the solder joints to crack much more so than when turned on leaving the gate. Remember the old tube TV's and even the news ones. Who's TV never dies? ans. the guy that leaves it on 24x7. When does it die, not when it's on, but when it is turned. How many times does an aircraft taxi to the gate OK, and break when fired up from cold for another flight.
