Worth powering up and gym rework

Why would that make powering up not worth while?

I think it's most likely that the CP will get multiplied by a number between 0 and 1 determined by current motivation.

In any event, powering up anything right now is a fools play - since we don't know how things will shake out in the rework.

Higher CP means it takes more to knock them down. It also raises their level which makes them harder to take down. They also get HP increases.

Big difference fighting a level 28 Blissey vs a level 38 Blissey. You tell me how that goes.