As someone who just got an update from Maddies home (it's been over a year now since I've rehomed her) I'd say yes, send an update. I get an email every couple of months, usually just a quick "We love her/she's doing awesome/we still are spoiling the crap out of her" and a picture, but like someone else said, I float for days after I get them. I worry about her constantly, but knowing I will get an update soon and knowing that they love her as much as I do really does make it easier.