I'm not sure if you've already made a decision regarding what to do with old/extra NIC cubes, but I thought I'd share what I did with the additional panels I had left from making my NIC pens.
I used the panels I had left to make organizers for the pre-existing shelves I have in my bedroom. They help make separating items easy and fun. And, for someone as OCD as I am, they look neat and help keep everything in order and easy to find.
Another idea that I put to use was to put them in deep dresser and armoir drawers to organize socks, underwear, bras, and the like. They also help keep smaller items in one place as additional storage cubes. I have a couple underneath my bed to hold exercise equipment, weights, and other miscellaneous things I've accumulated through the years.
No matter what, my suggestion would be not to get rid of them if you're ever planning on having bunnies in your life again. They certainly won't go bad and will always manage to find a use for themselves - especially if you're an organizing neat-freak like me! But if you must see them go, I second the suggestion about donating them to a rescue organization - you can never go wrong there!
Best of luck and let me know if you need any other little ideas...