Re: Should I hit the heavy bag...
I used to do the heavy bag workouts without gloves, wraps, etc. but that was only after five or six years of intense karate training (my sensei was old school and had us hitting a makiwara--look it up--several hundred times per day) and god only knows how many thousands of knuckle push-ups. That said, I *still* occasionally strained my wrists, though thankfully never anything serious.
You'll thank yourself a hundred times over if you work the bag with some nice 16oz gloves. The first time I sparred with a pair I thought my shoulders would crumble and fall off. I also felt like I was moving in slo-mo. Now, I'm better conditioned than I've ever been and can spar with my partners for up to an hour without arm and shoulder collapse. And, yes, my speed has increased dramatically as a result.
Long story short--these guys are right on the money. Even if you don't break a wrist, your opponent likely will break your face when after a couple of minutes in the ring you can't hold your gloves up any longer.