[kurious kat]

I think it's fine to reach out to someone and express admiration for the qualities you see in them. When a compliment is personal or thoughtful, it might or might not go anywhere, but most can appreciate their work being noticed.

I only find PMs rude when:

1. The person sending the PM asks for something that neither the recipient's profile, signature, nor posts suggest they're likely to be interested in.
2. The sender has sent a similar message to that person in the past, but ignores or forgets that they've already declined.