Using DispOrder overrides the mosaic method. Mosaic Method is only applied to records where the dispOrder is 0. To force images in a speciifc order set the disp order to a lower (negative value). IE set -1 for the 2009 and -2 for the 2005 images.
The MosaicMethod should also work. For example if you have a field called year, set the be Mosic Method to ByAttribute, set the Field to be Year and the Base value to be say 3000. Images should be ordered closest to year 3000 so long as they are in scale. Double check that the MaxPS values enable the 2009 imagery to be displayed at the smaller scales.