I grew up with the ‘Christmas Letter’. Mom sent out a recount of the year in the form of a letter tucked inside the Christmas card. I’ve always loved it. Especially receiving them, and just keeping up with friends. (of course, that was all in the days before Facebook, Gmail, and IM)
When I married and had a family of my own, I sent Christmas letters. Each year, I’d tuck away the special ones, just couldn’t bear to throw them out. From my parents, my sister, my kids.
Several years back I found a 3 ring notebook, and gathered all the copies of Christmas letters. I purchased a package of plastic sleeve page protectors, and sorted the letters by year. Wow, what an amazing history of our family. All the joys and trials. All the births and deaths. All the fun little things that kids say and do. All the achievements. And especially, all the praises to God.
I’ve always had the intent to keep a diary, but never got further than the ‘starting it’. My book of Christmas letters is our families diary. I plan to one day copy it and give it to my grown children. What a legacy, what a treasure, what a good idea!
49andcounting 
I started our family Christmas Letter 48 years ago. I have found copies beginning with 1967 and have put them in a notebook just like you suggested. I wish i could find copies of the earlier ones!