And in reality, selling one of those sleepers three days in advance of departure is going to be very difficult. I would prefer an overall no refund sleeper cancellation of, say, seven days across the board. If you cancel and it happens to sell, then you might get 80% of the sold value back as an e-Voucher, no guarantees.
The other thing is that coach and special redemption should allow no-shows the same way as paid tickets go - with points returned to the account. Because of this new rule, I have more of a tendency to book coach and special redemptions the day of travel (sometimes just a few minutes before travel), since Amtrak trains in my area rarely sell out except on blackout dates where redemptions don't work anyway.