... any admission that is more ...
There is one other thread going around where they are saying that "more" means "equal or more treating each feature, attribute, characteristic, and option separately".
From what I understand, that is:
If the original ticket had 3 days left, the new ticket has to have at least 3 days.
If the original ticket did not expire (all standard non-MYW tickets do not expire) the new ticket has to have non-expiration.
And also if the old ticket had so many dollars of value, there is no dollar refund in the upgrade transaction. (usually the dollar value remaining on the old ticket buys less Disney fun worth of new ticket compared with using the old ticket as-is)
etc.
The dollars you need to add to purchase the new ticket depends on meeting all of these criteria.
Finally, I am told that a ticket with some plusses but no days remaining has zero dollars of trade in value.
Disney hints:
http://members.aol.com/ajaynejr/disney.htm
Correct me if I am wrong, or perhaps this may all change after/as the bugs are worked out.