This whole over dubbing and live mistakes thing is normal, whether it is a good idea to overdub or not is down to personal opinion. I am watching a documentary about Tubular Bells, and the guitarist Jay Stapley was saying that he expects to make a mistake playing live, and if he hasn't it makes him more nervous, once he has made the mistake it settles and him and he can move on, this might not be the case for all musicians, but, I found it an interesting statement. Also, re-recording or overdubbing isn't always as great an idea as it might seem, the original Tubular Bells album from 1973 has lots of mistakes, out of tune instruments, out of time playing, but history has proved it being part of the albums charm, Mike decided to re-record the album in 2003 and made it perfect, it's sounds amazing, but there is definitely something missing, Mike admitted that the new version is hardly on display in shops, but the original is the 1st thing you notice!! So, things don't always need to be perfect, mistakes are nothing to really worry about.