Is Venusaur worth investing in?

Yes I love this moveset. Definitely worth investing in. Plus it's good to power up the only useful starter from gen 1.

My Venusaur is the only "attacker" i have powered up so far...

I was using Jolteons early on to deal with the mountain of Vaps, but had to always heal/revive so invested dust/candies into a Venusaur to be able to knock out more than 1 high CP Vap.

Grass types are also good for Rhydon so it has a dual purpose.

You really don't need to power up that many attackers so I'd save dust/candy for Machamp as well and use random evolves if candy/that mon is plentiful (like high level Eevees for Flaeron with FS/O).

Yes it worth to power up... Its a Vape, Rhydon and Tyran's Assasin...

venusaur is a beast, and even at ~2200, the AI always wants him to go first...even against charizards and the like. . .what gives?...

Venusaur is good for attacking into water Pokemon. Just make sure you know what role you want it to play. Is it going to be an attacker or is it going to be a prestiger? These two roles require different CP ranges.

Personally I have two Venas at 2100cp (VW/SoB and VW/PB) and one 1100cp VW/SoB.

Some of the attackers I could not live without.