Seb7 - 4:30 am on Mar 12, 2012 (gmt 0)
Could it be possible that meta noindexing product-level pages would actually boost ranking for category pages
I'm guessing you have links to the categories from the product pages; this is actually what is boosting your category pages.
I personally always recommend putting the entire product line online. But.. your titles, descriptions etc have to be directly relevant to the product, and web friendly. Linking correctly with category pages always works well.
(By web friendly; you need to think about what is the most probable search term someone would type as to find that particular product - its often not the same as the product description/name that the business has already for it. I often end up renaming 80% of the products before going live - and always had great success.)