I like Fathers Day and Mothers Day at the very least because sometimes it's an excuse for family to get together and anything that brings the family together for a nice meal and good times is good stuff in my book.
We don't get together every year on those days but often enough.
Plus some people need reminders and a push to let their parents know how much they mean to them. I can't imagine any Father or Mother minds getting a heartfelt card and a reminder they're appreciated. Obviously you shouldn't need a special day but it doesn't hurt.