Should I power him up, or wait?

Since the CP is so low, you almost need one with higher IVs. I've got two with 95% IV and Bubble/IP, but I still won't power them up because they aren't very high quality pokemon anymore.

Even perfect IVs, fully maxed out (lvl 39), it's like a mediocre Vaporeon.

It really depends on what do you want to use Poliwrath for? Different people play the game differently. If I want to stay in the gym as long as possible, I will put my highest CP pokemon - usually Dragonite or Snorlax so that I will sit at the top.

But in my area, even highest CP pokemon would not sit in the gym for long. There are residential areas around the gyms and others can just fight the gym from the comfort of their home.

I rarely see gyms lasted for more than 20 minutes unless you are talking about midnight. I have also never see a gym going above level 5. We just do not believe much in prestiging.

So sometimes, I just want a little change. I want to frustrate others when battling. In my area, not many people put Poliwrath even before the nerf and I suspect that they are not familiar with it.

My wife and I caught a 100iv Poliwrath with Bubble/Ice Punch at level 16. We max out the Poliwraths and place them in the same gym.

If my pokemons are going to be taken down within 20 minutes anyway, I want to make the life of opposing team as hard as possible.

I do not have a good Snorlax. And I think Dragonite even at high CP can be taken down easily. So Poliwrath is my next best choice.

He'll sit pretty low in a gym but does an okay job. I tend to put him in gyms that from past experience know won't last that long, or where the lowest level Pokes in the gym are lower than usual. I've powered mine up to a little over 2000 and will max him out when I've got spare dust.