Power up Sneasel?

Save your candy for the evolution. Once it comes out you can make your decision if you need them for your team.

Ask yourself, what would you use it for?

Nah, i'd power up them as weavile though

No real reason to power any pokemon up that does not have a current use. You can always wait until later. Power up guys to use for current and upcoming raid bosses. In this case; Dragons, Mewtwo, Machamp, and Dark TTars. If you don't have those guys, power up lesser pokemons of those types. Conserve resources!

Congrats with your catch! In principle I agree with the rest that it is advisable to wait until you have a need, but Sneasel is one of my favorites so I decided to slowly power up mine (via research tasks etc) so they be immediately useful once Weavile arrives

I have a thing for 100%ers, I have partially powered up perfect Ninetails and Pigeot. That said, however, I would also wait for the evolution to power up a perfect Sneasel. Congrats though, I wish I had one!

Not until we see what Weaville's moveset is going to be.