Most sandslash trainers simply throw them away, yes. Sandslash spikes are much like your fingernails. They’re largely made of keratin and soil, and thus, they’re not actually suitable for much besides composting. Other, more creative trainers do as you do and make jewelry or art pieces out of them. Quite honestly, it really depends on your taste, but I would recommend adding them to your compost bin if you have one. They make excellent fertilizer.