This article relates to a spate of robberies to motorists in UK plated cars using the AP 7 during the school holiday high season around the Barcelone and Valencia area. I've just driven down that route and across through Madrid with no problems and it was extremely quiet.
I would recommend avoiding stopping at service areas near major cities, don't leave you vehicle unattended if at all possible and watch out for people who are obviously immigrants moving around the country by blagging lifts from truck drivers. They tend to gather in numbers in some service areas and they are the ones who will try their hand at robbing tourists.
By the way the AP 7 is hellishly expensive on tolls especially around Valencia, might be worth seeking alternative. Jon Faulkner.