For planetary imaging you use a technique called lucky imaging, in which you use video and high frame rate (low exposure) to image.
So, if you requirement for a mount is limited to planetary imaging with the C8, then be able to guide is not a requirement.
But if you want to do any long exposure astrophotography you will need good guiding (at least as good as limited by the current seeing).
P.S. JMD, I hope you don't mind me answering the question on your behalf.
THAT was the conversation I was having in my head! Thanks John!