I have close friends that play for some of the top artists in pop music, period. I can tell you from knowing them as well as my own experience, that you are never satisfied. You always want something better and want to achieve bigger things. You are a wheel, and their is nothing wrong with that at all. You don't want to beat yourself up, but keeping yourself mobile and creative will truly yield you a result in some way.
Nice to hear that. This is happening to me all the time. I think some people think I have accieved pretty much but I still feel its not what I wanted or it could be better - and you are right you have to keep it up and go over the frustations which come back from time to time.
HP