I've been rereading Spock's Wold recently and there's a passage that talks about how very few Vulcans have ever left their planet, let alone their system.
So? That novel isn't canonical. Enterprise
showed us a Vulcan civilization with a large and active interstellar presence. That canonical evidence supersedes a decades-old novel, no matter how well-loved the novel is.
I'm not sure that novel even means what the original poster thinks it does. Spock's World
is a Duaneverse novel belonging to the Rihannsu continuity. In the first novel of that continuity, My Enemy, My Ally
, Ael reflects on the traditional Romulan attitude towards Vulcan and current-day Vulcan civilization: "The meek, after all, had inherited Vulcan; the Rihannsu had gone out and conquered the stars." Even there, there's evidence for a fairly significant cultural divergence.
(There also might not be such a contradiction between the depiction of Vulcan as isolationist in Spock's World
and the depiction in Enterprise
of a Vulcan with a substantial presence in space. How many Vulcans need to go into space, after all? An apparently prosperous and technologically advanced 22nd century Vulcan that was a status quo power presumably wouldn't need to commit very large amounts of labour to its project.)