Powering Up Golem

I think 30 is sufficient for now, save your dust for the legendaries if you don't have much.

Legendaries aren't that difficult since you have more time, and they usually attract more people to them, so one person makes up less of the total percentage of damage done, so the difference between a level 30 one and a level 37.5 Golem should be quite minor when it comes to a legendary raid, whereas for smaller raids, for example around 5 people doing a level 4 raid, the difference between a powered up Pokemon could be the difference between timing out or not.

At the moment, two level 30 double rock Golems might be more useful than one at level 36. The number of candies you will need to max this one is about enough to evolve another.