Do you think people would notice a miscalibration in the color of these Christmas cards? My guess is they wouldn’t. Unless you’re doing photo prints professionally the color issue is probably not a big deal. BUT, if you enjoy doing these cards and other hobby type photo stuff and it would bug you to have a mismatch, then I can see why you’d want a color printer. It’s just a matter of priorities I guess.
No, usually I have a photo on the front, but I don't care too much if the color calibration is completely accurate... that is one of the reasons why I use an online service to upload and print them... it is worth the 20 cents a piece to not deal with the hassles of trying to find special card stock, print out a hundred of them and then find envelopes that fit the finished product.
But some pictures that I take I do like to get the best possible results and then it is worth taking a little extra time. Its a hobby but I have to admit that most of the time I actually use a specialty photo printer for these which has additional color cartridges, but we print enough color on the daily use printer that I still appreciate having the feature.