Does anyone know of a good reason why, even if the intention is to print to grayscale, a CS4 file shouldn't be linked to colour images?
If the intention is to have grayscale output you pretty much need to use grayscale images. ID does not currently support export to grayscale spaces. You can print to composite gray, but the quality is not likely to be as good as a customized adjustment and conversion in Photoshop for the images. Likewise, you can use Acrobat Pro to convert a PDF to grayscale, but the same limitations on quality apply. What are distincly different colors in RGB or CMYK may have the same luminosity and wind up being the same level of gray in the conversion.
That answers my question precisely.