Is it worth to power up this??

It really depends on your goals. Do you want to defend gyms? If so Snorlax and Lapras are probably worth powering up. If you want to do raids, then Scizor is a great counter to Mewtwo and grass bosses. Gengar is also a solid raid boss choice, although he is very weak. Personally, I think that any 100 iv is worth powering up but it really depends on what you enjoy doing.

If Gengar has Shadow Claw (legacy) and Shadow Ball, or if you can CTM to Shadow Ball, then pump up the Gengar.

Scizor is not only a great current counter to Mewtwo, it is also decent as a generalists (lots of resistances and very quick moves for dodging), and is useful as a future counter for Mew and especially Celebi as well.

Furthermore, Scizor has the option of serving as a powerful Steel attacker as well, which will be helpful when the army of Gardevoirs comes into gyms.

Congrats, that's a great list of perfect. Power up all if you can.