You're thinking too much, lol. I typically like to have a little more space and capacity than what I think I'm going to need. Sure enough something always comes up that I'm glad I had it. I say keep it too and spend the money on another attachment or something instead.
If you're 2500HD is a gasser then the 10k rated trailer is probably about the max for your GCWR. That's why I bought a 10k equipment trailer and dump trailer when I had my GMC 2500HD. I don't need that capacity on the equipment trailer for my tractor and attachments but I planned for the max load for my truck and I have used it frequently towing other vehicles. I have since traded it for a newer Duramax but still use the same trailers. No need to upgrade them just yet, but I would never downgrade with either one.
Also, most car trailers have low dovetail on the rear for easier loading and unloading and are low slung. That may be a problem with dragging if you actually take it off road to load and unload the tractor.
Duramax. Simplest answer is always right. Trailer tows fine. It might make my life easier if I could minimize the appearance to my wife. It wouldn't really matter, she would not be able to move truck with any kind of trailer attached.