Hi Cyrus,
I'm also a fan of the phrase you mentioned ("if it ain't broke, don't fix it"). But in this case, I'd rather have category pages rank.
The tag page doesn't offer any content. It's just a product listing page (all pages tagged with the label "digital camera" for instance). So when a potential client arrives on the page, I'm not sure he'll find what he's looking for whereas the category pages offers good content, faceted navigation and so on.
Your suggestion, in short, is to make the category page look more relevant to Google for the keyword "digital camera" than the tag-Page?? So I should leave the tag-Page as it is (no 301 to category page??) and link back to the category page in order to strengthen it (several internal links pointing to the category page).. What about altering the meta tags of the tag-Page so that they look less lrelevant for the targeted keyword?
Thanks for your help Cyrus, I really appreciated your answer!!
Bye Martin