Convenience isn't an excuse to not encrypt security data, it does not matter if it is a limited to a few areas where it could be exploited. If Google (any companies, including Apple) can not be trusted to protect such information, they should not be offering it in the first place.

If it can be exploited, it should be protected as much as it can be.

We all saw what happened with Google's StreetView cars capturing the local Wi-Fi traffic. The same thing could be used by somebody hacking into Google's servers, downloading the Wi-Fi passwords and any possible maps data if possible and workaround getting into people's Wi-Fi networks. If it is not likely but it is not impossible.