I believe there are a few other discounts on staying at the park hotels including Triple A rates, Military Rates, and Senior Rates. There's also some local advertisements in the SoCal papers from time to time for specials although I rarely saw any of those.
From time to time you'll also see specials on their website and on travel sites like Orbitz and Expedia.
With the economy down and attendance down as well I'd say you have a better shot at seeing more discounts offered but I wouldn't hold my breath for more than a 20% cut especially during peak times. Looking for other types of discounts (like buy 3 nights, get 4) may also be a good bet.