I agree with Mike - I'm not sure I'd send a Valentine to a church leader or my boss. But your friends and relatives would probably appreciate the sweet gesture!
What about sending a post-holiday newsy greeting that lets people know you were busy at Christmas and you hope they have a wonderful year? Now that the flurry of Christmas is over, people will have time to read and savor your message even more. Everyone understands being busy; they'll just be glad to hear from you.