Viewers can learn a lot from short games
Never have I seen a 1v1 FAF-cast end with an early T2 TML snipe. Same for a zero-mex arty & com-rush on a tiny map.
Casts showing steamrolls and cheesy builds teach people about these. Also, we never see games where a player gets himself into a huge power stall which causes him to lose the game.
If we see this regularly in casts, then we will watch out better for it in our own games, which will improve our play. Aside from learning to defend or carry out cheesy builds.
I can imagine a caster saying "Okay, Strawman is going all-in on early Artillery. Whenever you see this used against you, all you need to do is... and you are pretty much guaranteed a win."
I also play Starcraft 2 and I have learned a lot from these short games and cheese. In Starcraft 2 casts are usually from tournaments where every single game is cast, no matter what cheese was used or how much it was a steamroll. Especially for ladder.
No pre-screening or casting series of short games
Not pre-screening ladder games would already be a good step forwards in this respect. BRNKoINSANITY's ladder stream is also good. He just streams, so if he is cheesed we see it happen, and we get to see how to respond to that or how it works.
Occassionally making video's with 2 or 3 small casts would also be great to see.