Bob, generally speaking it's best to redirect users to the page that's most appropriate. Think of the users and what page they would land on--and be redirected to. If they were looking for an old product page and just redirected to the home page, would that be frustrating for them?
When it comes to an actual search engine ranking lift or boost, you most likely won't see one. You only would just not rank anymore for those products that you used to offer. There still may be a boost if you were to redirect an old product page to another page and there were links pointing to the old product page from external websites. Then, the boost might be passed on to the product page you redirect to.