Some, yes. I don't think so many as to make such a big difference.
DRSislove, you saw Brian's 3rd performance. Sure, one should be great as soon as they start, but it's natural for actors to improve as they get more comfortable with a character. I saw Brian a couple times after, and he was much improved, while Keith was tremendously improved. Pryce wasn't exactly getting raves by the time of his third performance, and look what happened to him.
And I do agree a good cast is important for the show, but I think we all define good cast differently. For instance, I was fairly disappointed in Richard Kind's Andre...slightly biased but still in general, but I took my friend who never saw the show and she thought that he, Keith, Brian, everyone was great. There is such an immense talent pool of stage actors that I can't fathom only those couple of actors part of the OBC can make the show.
Again, it's important to remember the differences in perceptions between people like us who had the pleasure of seeing the Broadway cast multiple times, and someone who has never seen the Broadway cast and the touring cast will be the first cast they ever see perform this show.
"If there was a Mount Rushmore for Broadway scores, "West Side Story" would be front and center. It snaps, it crackles it pops! It surges with a roar, its energy and sheer life undiminished by the years" - NYPost reviewer Elisabeth Vincentelli