mrchi wrote:
What I would like, ideally, is not to have to use this MP Navigator EX thing at all, and just a basic scanner driver. Is that what 'ScanGear' is?

I've never liked the Navigator application and have only used Image Capture and Preview in OS X 10.5 and 10.6.
ScanGear is the scanner driver/interface that apps like Preview use to provide extended functionality, like resolution selection.

To remove MP Navigator EX and start from scratch is it enough to just drag it out of the Applications folder? Or is there more to do?

Pretty much. There are other files in your Mac relating to the Navigator app but trashing the file from Applications and then emptying the trash should suffice.

Will Bonjour offer me ScanGear if I plug the scanner in by USB after removing MP Navigator EX?

Connecting the scanner to the Mac via USB has nothing to do with Bonjour - that's a protocol for network devices. But yes, if you connect the scanner to your Mac you should still find that the CS8800F device located in Print & Fax still functions fine without MP Navigator installed.