I am thinking that you could add the "chain link" icon where the "1" is in the first attachment to manage the links of products to the resource. Clicking on that link would show a field similar to the Related Products box, where a product could be added to the collection.
The Resources would then be linked on the respective Products on the Media tab just as they are now.
This is essentially working in the other direction as adding Resources now. Instead of adding resources to products, you can add products to resources.