If I understand the question correctly, it sounds similar to how most eCommerce sites deal with sub-category (e.g. Apparel/Clothing/Pants) and you're asking if you should put unique content on those pages.
There is no right or wrong answer here, but I have two guidelines for you to consider.
#1 Search Volume
Does the topic of the category / inventory page receive significant search volume? For example, if it is a landing page about a brand-specific product (e.g. Used Honda Accord) it probably deserves its own content. If nobody searches for the exact product assortment that page is about (e.g. blue used Honda Accord year 1989) then you may not need the content to rank for those long-tail queries.
#2 How Can You Help Your Visitors?
The primary goal of content on these pages should be to help the visitor. Improving your rank for searches should be a secondary concern, which will alleviate some of your trouble with pushing the listings further down on the page.
Think about what the user is trying to do on this page. Most of the time they're still not sure exactly WHICH product to choose, or they'd have landed on a product page, or a deeper category. Help them choose. For example: Brand X is for entry-level shoppers and provides the greatest value. Brand Y is for experienced shoppers and has the most features.
You can use drop-down divs and other display tactics to keep from pushing the listings down too far.
You can also prioritize these pages so you're not writing content for all of them at once. By focusing on the top performing 20% or so first, you'll find out if the investment is going to scale out well to the rest of the pages, or if you should just leave them alone.