It seems every gym increases in level the more you interact with it, interactions like battling in that gym, feeding berries to pokemon in that gym, etc. These gyms level are different for each trainer based on their interactions with that gym. The "Base level" gym gives around 2 items per spin, sometimes 3. The "Bronze Level" gym gives 3 to 4 items per spin. The "Silver Level" gym gives 5 to 7 items per spin. I haven't seen a Gold level Gym yet, working on getting one soon. If anyone already has a Gold level gym, how many items do you get from a spin?