+/- I'm looking at this only for HG
It would be amusing to spectate HG games, but a majority of them are pretty short as there are games varying from 1v1's to like 6 people in a game, so it wouldn't really be necessary.
I'm all for a toggle option though, where we can toggle whether or not we would want to spectate a game. This way neither side is restricted to only one way of doing things.
For giving tips, most of the time you can fight them, defeat them, and them give them tips based on their skill and way of fighting. Not really sure if a spectator mode is then so necessary.