Read lot about these 2 directories on this forum and also when buying link make sure pr of that page should be high and less numbers of links on that page. But on checking these directories in shopping-jewelry category, there seems to be hardly any advantage for spending $50 for getting listed. http://www.avivadirectory.com/Shopping/Jewelry/ http://www.alivedirectory.com/Shopping/Jewelry/
You do have a valid concern as overload of a category is a problem that every directory faces. But alive and aviva are a little different. It may not be always about the page rank, if a site is conidered a authority site (in this case both the mentioned directories are) one may alwasy look in the listing as adding value to a submitted websites SERPs.. Depends on what you are looking to achieve, a SERPs advantage or site visibility ? These directories can give you the SERPs advantage at the fullest, irrespective of the PR of the pages. But if you are looking for more visibility, you can look for a buying listing at a more visible and niche website.