I have to be honest. We send about 55-65 cards. Any where from 3 to 6 packets are separated by what we know about our friends. One or two packets are religious. If we know they are a member of a church (many of them are) or of my wife's church (we belong to separate ones - that's another story), we send one that says something like "Have a blessed Christmas", and has an inspiring picture on it, and we write a small personal note.
Of course we have some dear friends who are not necessarily Christians. (We were both teachers and made a lot of friends down through the years and still stay in touch with many of them - some are Buddhists, some are Muslim, etc). But we still use the word "Christmas", and they have accepted that and understand us,
just as we do them. (If they didn't, then they don't know us, and probably would not send us another card - we go over the list every year and add or delete as the case may be, just as I assume some of them also delete us.)
So we spend a lot of time on our Christmas list. Always have. But we take a lot of delight in this, and don't consider it a chore.