I've thought about that as well. I tkink they might be a bit of a problem in a typical GA cockpit, with limited head and shoulder room. If you end up in an upside-down situation, that might contribute to your death by bending your neck in ways that cause asphyxiation.
Also, most flight helmets (at least the ones I'm familiar with) don't seem to offer that much face protection, which is the main way we get head injuries in GA accidents. With some you can install a nose/mouth shield, but not sure what kind of impact that is rated to.
Drifting this topic even more, how about wearing a nomex flight suit? A lot of survivable GA accident end up being deadly (or with horrible long term injuries) because of the post-crash fire and the resulting burns over 80% of the body. A flight suit would offer enough protection for a surviver to get out, maybe in combination with gloves and a cotton balaclava.