Venusaur with Sludge Bomb

I would - it's a decent defensive move set.

It's the best defensive moveset. But venusaur is not a very good defender, and his CP are not very high, especially after the recent CP update, he is far behind :
Dragonite, Gyarados, Snorlax, Rhydon, Vaporeon, Lokhlass, Golem, Exeggutor, Flareon, Jolteon, Arcanine.

So, like Poliwrath and Slowbro, it's gonna be very difficult to be in a good spot in a gym.

It's up to you but I wouldn't power it even if I love Venausaur. I stopped powering up my 93% one.
I would keep it and pray for a buff in the future.

I also have 96% with same move set and i dont power it up, imo.

I would. I'm sure I'm not the only one appreciating a cool high CP starter mon in a gym. Great to look at, great to battle against. And your Venusaur is ment to be a defender: high IVs, best defensive moveset.
Let him fulfill his destiny

I have a 100% Ivysaur with enough candies to evolve him and power him up to about level 25. I plan to take him all the way. Yeah his CP isn't very high now compared with others but he's super rare here. I might see one a week max in gyms. Yes they aren't as good with the slight nerf but they are so rare.

So for that reason I'm powering mine up. He's one of my favorites so why not? All depends on what you want to do and if you want to spend the candies and dust.

I'm hoping I get a good defensive moveset on mine because I plan to put him in gyms.

I've got a 98% Venusaur with Razor Lead+Sludge Bomb and I love putting him into gyms. Sure his max CP is not as high as the most common defenders, but when I come across a gym that is not already stacked with just high CP Rhydons, Vaporeons, Gyarados, and Dragonites, then I like putting some more diverse pokemon like my Venusaur and Machamp that I have "wasted" stardust on to bring them up to 2300+ CP.

If you are not short of stardust, definitely power it up!
A perfect Venusaur has 2200 CP @ level 30, that's not too bad actually!

I love Venusaur, in fact I'm one of the rare people who loves Venusaur more than Charizard and Blastoise and used to always choose bulbasaur as my starter mon. I've powered up my 93 iv Venusaur with the same moveset as yours up to lvl 31 until the recent nerf, I've stopped powering him up for now (hes 2300 CP). I think I'll probably max him once I hit lvl 39 or something but in the meantime I want to maximise my offensive and defensive team focusing on high CP pokemon that I also like.