Wow, what a spirited discussion.
Here's the story in a nutshell:
An unexchanged voucher for and AP/PAP/SP can indeed be used towards the purchase of MYW tickets instead of being redeemed for the Annual. The only stipulation is that you must purchase enough MYW tickets so that they total more than the value of the exchange voucher. They will apply the value of the voucher towards the transaction and then you pay the difference. There is no refunding and you cannot just exchange the voucher for a single MYW and say "I don't care about the price difference. Keep it."
I include my usual caveat on non-standard Disney ticket transactions: You may find that the policy described above will vary from CM to CM. Some will do the transaction with no problem. Some will say it cannot be done. Some will never even have heard of it. If you have a problem doing this, ask for the CM's supervisor. It most definitely can be done.