That's totally up to you. If you find value in it, then it's worth it. Historically, though, the latest expansion goes on sale before the new expansion comes out. If you can wait four months, it is likely to go on sale and be a lot cheaper.
If you want the house and the fluff, its worth it, but I would wait until October when it should go on sale, usually about a month prior to the launch of the beta for the new expac that comes out in November.