I've scanned the entire PDF manual for both the 500 and 900/90 units, and don't find any reference to 'elevation'.
Every GPS system, in-car or otherwise, factory or aftermarket, has supported some manner of displaying the elevation as measured by the GPS on the screen...I want to buy one of these AVIC's but do a lot of driving in the mountains where elevation is worth knowing.
Surely this is a feature...?