I have one of those AP back protectors. Haven't had any crashes where it mattered yet, but it feels unrestrictive enough.
I often think about how dangerous motocross is, and I think it's a bit silly to bring in arguments like "you could get run over crossing the street", since MX and enduro are statistically quite unhealthy.
I have the need for speed so bad that I would go insane if I couldn't ride, so I wear all the protection and take all the precautions I can, and go racing, acknowledging the fact that I may be permanently injured any day (I have been around MX tracks all my life, and have seen one kid's share of people who will never ride again due to an MX injury. Very few of them are bitter or regret that they chose dirtbiking).