Battling gyms up is really slow and painful now. I give up Happy to jump up on a gym level 1 to 3, but any higher than that and it just takes too long to raise the prestige.
On the other hand I started to pay attention to pokemon types and which pokemon is best for a particular battle, and that's good fun. My fairly low CP Victrebell can battle much stronger Vaporeon really well. And my Dewdong (only CP 1300!) is good against fire pokemon like Dragonite.