If Spock has been having dreams of angels since he was a kid, I could maybe let it slide that he never mentioned it to the Enterprise crew (he didn't want them to think he was crazy), but it's practically unfathomable that no one brings it up in Sybok's quest to recruit the Enterprise to find God in Star Trek 5.
Except that nobody in that movie knows about it, except Spock, who tends to hold his cards close to his chest. Nobody in Star Trek V knows about Sybok until Spock fesses up, so maybe Spock never mentioned his childhood visions to Kirk or McCoy.
Granted, it's hard to say until we see how the Red Angel storyline resolves, but it's possible that Spock's childhood memories are his own private affair, like his fiancee, pon farr, his katra, etc.