Power up Victreebel?

Use the CP calculator to figure out how much it'll cost you to power it up to whichever level you want. We don't know the level of the Victreebel just from its CP.

https://pokemongo.gamepress.gg/cpcalc#/

While Sludge Bomb is the worst attacking moveset against water types, but it's still a usable move even with only neutral damage.

I wouldnt hehe...not very usefull if you have an Exeggutor Zen/SoB or a Venusaur. 1300 to 2000+ cp will cost you lots of dust for a 76% IVs. Any hatched Bellsprout level 20 can evolve to a better IVs Victreebel...its not rare so you can keep it untill evolve a 90%+ iv with the same moveset.

If you'll use it regularly it's worth the dust. If it's only going to get occasional use probably not. The IV's are good enough.

Don't waste your dust for that. Like TheFocke already said, wait for 90+ bellsproud is very common. You will definitly get a better one with high cp soon.

No. Victreebel isn't even the best grass Pokemon, and 76 IV's isn't exactly amazing.

He's a better prestige Pokemon anyway so use him when you need a team to attack 2500ish gym defenders. He'll prove useful vs. Vaporeon/Blastoise, but that's about it.