Does this Gengar have value for power up?

Yes, any gengar with SC is worth power up.

For sure, Shadow Claw is leagues ahead of Gengar's other 2 quick moves. If you look on raid simulators, Shadow Claw + Sludge Bomb / Shadow Ball is normally like 10 seconds faster than the best non-Shadow Claw moveset (most of the time that's Hex + Shadow Ball).

On top of that yours has great IVs. There's IV snobs that only care for 15 attack, but all it's going to cost you is one extra power up to hit a damage breakpoint, which isn't much. You can "fix" IV deficiencies with extra power ups but there's no fixing a Hex or Sucker Punch Gengar into a Shadow Claw one.

Depends on what you want to use it for. Shadow Claw/Shadow Ball Gengar is amazing for soloing Gengar/ Alakzam raids, as well as Mewtwo raids, provided the last 2 don’t have Confusion. I powered mine up and never looked back. That being said, I rarely use it outside of those specific situations.