Are there any philosophers who argue that novel experiences in themselves are good things, or do philosophers generally class some experiences as good and others as bad?

This is a great question that invites a long, thorough answer, but alas I'll be brief. It's easy to recognize that things, events, experiences, have many different properties, and rather than try to evaluate the whole package and say that "x is a good thing," we can evaluate x along its many different aspects, properties, etc. So we could say that, in general, novelty (of experiences) is a good thing (for whatever reasons), while recognizing that not all novel experiences are "good things" overall -- after all, being tortured may be novel but few except masochists would say their new experience of being tortured is a good thing. Perhaps insofar as it is novel, it is good (b/c it's good to learn new things, have new experiences, etc); but insofar as it is terribly painful, it is bad; and in this example, since the badness of the painfulness outweighs the goodness of the novelty, the experience overall is bad -- even if novelty is, in general, a good thing ...

hope that's useful!

Andrew