Extend User class to include email and photo_url

I have extended User class to include email and photo_url. But there aren't many emails, only few contacts seems to have emails there.

Do you think that the only other way how to get users email is to use G+ API? Btw. which part of user_id should I use while linking to G+: chat_id or gaia_id? I don't see any difference between them, both seems to be same in every case.