As to viewing cards, I think that may be a bad route to go down. It may end up creating too many ways to cheat, or for friends to work together to give one of the players an advantage.
This is very true. Even if we restricted spectator chat to their own channel, friends on instant messengers or even if the same lobby could relay info about opposing players cards if they could see them.
One way to prevent cheating (i.e. open up another browser and spec your opponent) is to ask permission to see his cards.
That way, for example if you know that player (spectator), you wouldn't mind him looking at the cards. If a guest user asks you, you would decline if suspicious
Even if permission was granted, the ability to see those cards could allow the more vocal spectator to call move/suggestions for the player they are watching, which begs the question "Who am I really playing against? This rank 900 or the rank 1200 who is coaching him?" Granted, there are always other ways to communicate that info, but preventing it within game makes it a little more difficult and costly on turn-timer than simply being able to see cards directly.