You are eliding two different kinds of goods here: units of housing, and land. The average price of the former would presumably decrease. The average price of the latter would presumably increase, since loosened restrictions on development would make it possible to build more units of housing on a given lot. For current owners of single family houses, it's likely that the land price effect would outweigh the unit effect, although there will be exceptions (the dynamics of exurbs will be different from those of central areas, for example).