Cedar Planks - Reusable Vs. Disposable
The whole idea of using a cedar plank is to char the heck out of the bottom and produce lots of smoke and flavor. My roughly 1/4 inch planks are usually charred pretty well and I simply couldn't see using them a second time. At times, it seems that 1/8 inch or more of the bottom is gone.

If you find a good source for your planks, they should be pretty inexpensive so why push it? I found one of the best sources to be my supermarket right next to the fish counter. $3 - $4 / plank. Seems like a small price to pay when you are grilling a $30 piece of salmon on top of it.