If the weather is 25 deg. C and dry, then the Pitot heat won't usually be required unless you plan to go IFR, but if in doubt, then turn the damn thing on. If having it on burnt out the heating element, what the hell's the point of having one? I have to say I've never noticed, but what's the average life of the pitot heat anyway?
Pretty long I would assume, as long as you have some airflow over it and don't let it just sit there on the ground heating away.
With regards to radios, I always like them on at this time of year for the reasons already stated, but I also like to know that they all work before going off, just in case you need them.