As noted before, the RPZ lets you buy the option to use your car on a weekday.
It's hard to say that this devalues a house.
After all, people will spend thousands of pounds putting in a driveway for having that option. That's if the council will let them -pesky "listed building" and "conservation area" rules stop you knocking down walls in the core of the city just to park a couple of vehicles.
Take, Clifton, for example. In one house they had to stick in the driveway, then apply for retrospective permission to widen the gates to fit a double push chair in, one that turns out to be smart-car shaped.
Why would anyone go to the effort of filing multiple (refused) planning requests to put in a driveway, then sneak one in -along with a dropped kerb- just to get a car in? It's because having that driveway lets you park a car near a house.
That's why having a driveway is considered so valuable that Estate Agents mention it in their listings of houses in Clifton.
An RPZ can deliver that guarantee of parking to an area -by removing weekday commuters, and by placing an upper limit on vehicle ownership per household.
Given that guaranteed parking increases the retail value of a house, it's hard to defend a claim that an RPZ will decrease the value of households.