Pokemon Go

[Zippo]

Is it worth powering up Pokemon before evolving them?
I've been putting off evolving my Pokemon and focussing on powering them up instead but after seeing someone's Eevee jump from 400-something to over 1000 after evolving into Vaporeoen I'm wondering if I've actually been holding myself back by not evolving sooner

Neither
Only evolve "commons" in order to gain XP (while using a lucky egg) and do not evolve any others until you reach level 30 which means you should be finding the strongest versions in the wild.

Then you can evolve your best and then spend your stardust raising them even further.