Is there any way in the webform module, to cause elements, or perhaps all those belonging to a fieldset, to be hidden if a certain value is set in a previous element?
Yes, there is a way. It's called Google. Try this:
http://www.google.com/search?q=Conditional+webform+elements+drupal
I just searched on your Subject line plus "Drupal" and the second result is the Webform Conditional module.
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