I don't know how effective these would be given the requirements.... that being said I like the idea. I've had a different yet similar idea for a spell for sometime that would deal damage sequentially left to right on the board (or right to left). Deal 1 damage to leftmost minion, 2 to the next, 3 to the third, and for as many minions there are on the board.
The card would be called "Cascade - Deal sequential damage across the opponent's board starting at 1 damage"
Perhaps you could choose which side of the board on which to start the Cascade, however this might be a bit difficult to play around.
Not quite like the straights idea, but made me think about this again.