2.) How do soldiers perceive the power of a round, when only a very tiny proportion ever see their rounds hit a target? The highest rates of fire are used for suppression, where they can rarely, if ever, see an effect.

In terms of gun culture it is interesting to note that the perceived lack of effectiveness of 5.56mm is a mostly a unique US issue. I have asked every Israeli, UK and even South African combat experienced soldier I have interviewed in the last three years, and none of them have said its an issue.
Only one of the 14 SOG veterans I talked to ever raised it, and the IDF guys only pointed out that they liked 7.62mm for GPMGs because it went through walls better than 5.56mm SAWs - as did the US OIF guys I talked to.
Ding....ding.......ding. I've heard myself saying the same thing to folks who are dismal on the 5.56 and never carried the weapon before.