I woud also suggest a valuation discount because GPUs have a fixed expiration date. Mileage expiration can be extended indefinitely, so if a mileage upgrade doesn't clear, it's not a big deal. If your GPU doesn't clear, you may have lost the opportunity to use it.

For you finance folks out there, you could think of a GPU as a call option with a fixed expiration date. As you move closer to expiration, time value decrases, decreasing the value of your option (all else equal).

That's why you frequently saw people literally giving away near-expiration GPUs and RPUs in Coupon Connection....they basically had no value to the holder.