When it comes to SEO I tend to err on the side of caution and ensure that individual pages closely match, but not duplicate, the categories in which they are located, in addition to including a breadcrumb back up to the main category.
The breadcrumb serves two main purposes, firstly it allows the site visitor an easy to use navigation system to get them anywhere they need to be on the site and secondly, it allows me to show a reasonable amount of internal linking to allow the search engines to determine what the most relevant sections of my sites are for specific search queries.
For example:
Pets >> Dogs >> Dog Leashes.
Pets >> Dogs >> Dog Bowls.
Pets >> Dogs >> Dog Toys.
Pets >> Dogs >> Dog Food.
The higher the level of navigation, the more 'loose' my SEO work is, while still being general enough to get ranked, one level down, I tighten up the keyword density and alternative keywords, while on the third level, the keywords are all specific to that category or a specific page.
In addition, I make sure to include 'question keywords' as part of my SEO work as they seem to be getting more relevance than just your typical keywords and search terms do, at least in my experience.
So on a page about Dog Toys, I make sure to mention somewhere 'Where do I buy dog toys from' or 'what's the best place to buy dog toys' that way the page can be seen as an answer to a Google users question, not just an outlet to grab traffic and generate sales.
Hope this is of help
