I try not to regret selling any board games, but I don’t always succeed. I’ve regretted parting with my copy of Renegade Legion: Centurion, one of the first wargames I played (around age 12-14), so I bought a used copy.
One of the joys of buying used games is finding treasures like this in the box: handwritten Centurion stats on the back of what’s either someone’s homework or a piece of scrap paper their parents gave them.
My kiddo and I have had a ton of fun playing Car Wars 6th Edition together, and I’m hoping that a heavier game like Centurion might be a possibility in the future. The “damage stencil” system in Centurion (and Interceptor, I believe, though not Prefect; I’m not sure about Leviathan) is so cool, as are the little fold-up tanks.
The Unlucky Isles [affiliate link], the first system-neutral guidebook for my Godsbarrow fantasy campaign setting, is now on DriveThruRPG.