Hi James,
In response to your first question, have you tried converting the mosaic dataset to a new single raster? I've used the Mosaic To New Raster tool before to create one tiff file out of my mosaic dataset. Then I used the new tiff in a new mosaic dataset with other rasters. That seemed to work well. The only thing is any color correction for the new tiffs you're creating has to be applied prior to creating the tiff, so if your current mosaic datasets need color correction within them currently then you should do that before. But you can apply color correction to blend each of the new tiffs into one another in the new mosaic dataset.
Jenn