OP, if it helps, I am one of those people who loathes surprises. I like to plan everything. I won't go into detail on past surprises that flopped.
My SIL lives with me right now, as my brother is in Afghanistan. There is no way he will be home for Christmas, but if he were to surprise us with a holiday visit I would be thrilled. Out and out thrilled. We'd have to peel some more potatoes and put out another plate, but I'd adjust, and do so happily. I'd probably put together a gift quickly, even if it was some online music account prepaid, printed off and tucked into an extra Christmas card. I guarantee he'd receive quickly drawn and sealed with a kiss pictures from my daughter. In short, we'd make do and be happy to.
However, if he told us he was coming, then we made plans for him and ended up having to ditch the plans closer to the date, the disappointment would be bitter.