Power up Venusaur or not?

Solar Beam is better, and Venusaur won't sit high in gyms.

It is worth if you need a water counter. If you don't need it I would hold off.

They can take out 2-3 water rock pokemons by themselves. Thats a good attacker against current meta.
idk whats the level of your pokemon tho

I don't know about razor leaf, but I have a Vine Whip/PB Venussaur and it is pretty good against a Gyarados, for example.

IMO it comes down to candies. SoB is really the move you want, but if you dont want to roll the dice, you can roll with that one. I have a vw/pb one at 2200 cp and just got another one with rl/pb. I wont be powering up my new one because I prefer Tangela with SoB.

If you are looking for a grass attacker, wait for a V/So Venusaur or E/So Exeggutor.

If you are looking for a high IV trophy, sure, go for it. I have a 98% R/Slu Venusaur (best defensive moveset) that I have powered up pretty high and occasionally put in lower CP gyms. Petal Blizzard used to be a two-bar charge move which was a lot better for defense though. I don't know if Gamepress' ratings for Venusaur have been updated or not yet. Not sure how the shorter less telegraphed Petal Blizzard compares with Solar Beam at the same energy cost.

I would, I like that move set.