Something from Mousesavers that was posted elsewhere:
Using Walt Disney World Tickets at Disneyland
You would have to do an analysis to see if the price you paid for the WDW tickets is worth spending at DL. Plus you will have to go to the ticket booth everyday.
Using Walt Disney World Tickets at Disneyland
Interesting, unpublished fact: you can use any unexpired, leftover days on a Walt Disney World ticket at Disneyland or DCA! Present the Disney World ticket at the gate on arrival -- they will take it somewhere, deduct a day from it, and give you a one-day Disneyland Park Hopper ticket. You can repeat this day by day until the Disney World ticket is used up. They will not give you a multi-day ticket all at once, even if you have multiple days left on your Disney World ticket. Also, MouseSavers.com reader Danny P notes that any Disneyland ticket obtained from exchanging a Walt Disney World ticket must be used on the same day it was exchanged.
This policy has been in effect for at least 5 years, and the information was last reconfirmed by a MouseSavers.com reader as of December 2007.
Disneyland tickets are NOT accepted at Walt Disney World, and Annual Passes are only good at the park where they were purchased (WDW Annual Passes are NOT good at Disneyland, and vice versa).
You would have to do an analysis to see if the price you paid for the WDW tickets is worth spending at DL. Plus you will have to go to the ticket booth everyday.