GhostofCain
Ancient Mariner
You're right. The atmosphere seemed to be good early September, although Clive still might have been getting used to his new kit. Who knows what happened after Robert left. At least Clive didn't see a change in atmosphere until he returned from the UK (I find it hard to believe that he lied about that). Personally, I haven't heard Clive making obvious mistakes. I know that Steve could have judged this way better, but if anyone would point me out to a recording with an unstable Clive, I'd like to hear it myself as well.
I guess that Clive's writing was on the wall at some point during the North American tour; the fact that Nicko (allegedly) stood in and did a great job at that could have been what made Steve realise whom he needed for Maiden.
Regarding Clive's playing, we also have Bruce's criticism of that. If I remember correctly, he mentioned that at one show he was playing so slowly that he jokingly brought a pillow on stage.