If your tower is less than 8, putting it to 8 isn't likely going to save you. Since Commons with a rigid condition have a tendency to flood your hand (and that's when they're -not- Durable), I don't think anyone would take this into their deck.
However, it might be interesting/useful as a card that gets drawn through other means, such as Wind. (No, I am not suggesting we create underpowered cards for this or any other purpose.)
Still, 8 seems an odd value. If I'm playing my tower attacking deck, I'm usually ready to end the battle at 10 tower. Also, I'm figuring most players would have it target itself for the discard unless the situation calls for its repeated use.