Vileplume : Worth it?

What cp is it? It is always good to have a back-up grass type. Tho I prefer acid as a quick attack, that isn't a bad Vileplume for attacking. IVs don't matter nearly as much when it comes to attacking(and that isn't a bad IV either.) I will say that Vileplume isn't my first choice of grass types, but sometimes you just have to work with what you have. With so many water pokemon out there, it will still be very useful. It all depends on your situation.

It really depends on what CP he is right now, but I wouldn't power him up anyways, his not a really strong Pokémon plus 74% IV, it's just not worth it investing stardust on Pokémon with this type of quality.

Another post without all info we need, it's getting annoying. I am level 25 and my Victribell with Raz/Solar is at 1200CP and while my best Pokemon are at 2k I always power it up if I can because it simply destroys any water pokemon.

Depends on what you need it for:
Are you trying to take out enemy gyms with 5 Vaporeon defenders? Power it up.
Do you want to level up friendly gyms with a Vaporeon in slot 1? Leave your Vileplume low to maximize prestige gains.