The usual issue brought up with specials that affect the board is the question of how they would work for a defense team. I don’t think they’d be easy to set up and use as a hero power for that reason.
As battle items though, they could work. There’s already a limit of four items that can be used in events and against titans, so there is already a built in restriction to stop the use of such items getting out of hand or giving too much of an advantage to the user in a monthly event.
As for the specific proposals, if I understand it rightly after being awake 17 hours, ‘renew the board’ is fairly close in effect to the current tornado.
I’d also suggest that a Create Gem item/power, though the original post didn’t suggest that idea, would be too powerful. Create Dragon Tile might not be overpowered, though I’d suggest limiting it to one or two uses per battle tops.