I would divide the cost of it plus the cost of upkeep, insurance and gas (4 mpg vs. 20+ in our car) and the parking cost, both when you're using it and when it's just being stored (many neighborhoods don't allow them on driveways), and I would figure out how many nights of average price motels I could get for that instead.
Someone else cleans the room and breakfast is often included. We used to camp when the kids were young, and I reached a point where I had enough of cooking, cleaning and child tending under conditions that were more difficult than at home. I wouldn't consider it a vacation at all. But that's just me. Hope you enjoy your RV and get many happy miles out of it!
Something about this thread reminds me of an old Lucille Ball movie that we went to see at the drive-in when I was a kid. Gosh - I hate to admit I can remember that!
http://en.wikipedia.org/wiki/The_Long,_Long_Trailer