Some weird beardy man will give you store scrip based on the power of the rbelt turned in. Gain enough scrip to exchange for a belt of guaranteed power, if not usefulness.

Almost like adding soul stones and retaining a bit if their power, until you use it?

Yes, it would add a small bit of dynamic interaction that are soul stones bread and butter. Useless rbelts are almost a trope of the game I always felt even though the excitement from the magic red text is always fun. Some way of limiting them from becoming an endless chain such that the store belts wouldn't be accepted nor damaged original ones would probably be wise.