I do think that a clean performance benefits a newcomer more so than an established contender. If the novice falls the judges will tend to say, "Well, she's not quite ready yet," and her PCS will suffer from that perception.
I think that the seasoned veteran is more likely to get the benefit of the doubt: "Yes, she made some technical errrors, but we all know how good her skating skills and musical interpretation are."
Yes, people, including judges, do tend to see what they expect to see.
Of course, if a skater is capable of really good skating skills and musical interpretation, quite likely she will exhibit good skating skills and musical interpretation even in performances with a couple of mistakes.
Not every performance is identical, but the ones where the SS and IN are below par for that skater (might still be well above average) aren't necessarily the ones with mistakes. Sometimes skaters skate cautiously in order to avoid mistakes, and as a result the SS and IN are weaker than performances where they just go for it, missed jump here or there be damned.
And sometimes they're just really off and everything gets negatively affected. Other times they're really on and everything is working its best.
Which is why ideally judges should be evaluating each component on its own merits in that particular performance and not automatically lowering PCS for performances with visible errors or automatically raising them for performances without.
That goes for newcomers as well as established veterans.

