While I'm not exactly an "all the gear, all the time" sort of rider, I do have limits. I bought a modular helmet (one of the full-face with a flip up chinbar things), and if I'm going over about 25mph I make sure to keep the visor down. Why? Well... because there's a crack in it. One cold morning I was riding along with the visor down, and the truck ahead of me kicked up a pebble. It hit hard enough to put a divot in the visor. If that visor hadn't been there, it would have caught me right at the bridge of my nose. At 35mph, that could easily have done enough damage that I lost control and went off the road. I wear gloves with armored knuckles for much the same reason; pebbles and junebugs HURT at 40+ mph.
I have a Tourmaster Draft jacket and pants, too, the nice mesh ones with armor everywhere you really want it. Until recently, I always wore the jacket, but only wore the pants if the weather was questionable or cold, or if I knew I was going a long distance or at higher speeds than in town. A few months ago, though, I moved near Boston. There's heavy traffic all the time, and, well, Boston drivers are notorious for not seeing little things like motorcycles, 18 wheelers, and occasionally buildings. So I've made the decision to wear all the gear every time I go out. I'm not sure how long it will last, but I hope to just make it a habit.
Here's the thing: out in Amherst, where I used to live, it was rare to get caught in traffic. Sure, there were stoplights, but it was pretty unusual to have wait through multiple light cycles to get through. And as long as I keep moving, airflow through the gear keeps me almost as cool as if I wasn't wearing it. But... well, near Boston and Cambridge, I spend a lot more time sitting and waiting. And my gear is black.
I love my gear, but I may need to replace it with something lighter colored. Being delirious from heat isn't going to make my riding any safer.