Here's all my suggestions:
1. If there's a way to get pokemon to spawn in a specific region, try doing that. It's hard when you go to spawn to see all these level 40 pokemon come at you.
2. Some training events. Like you could allow someone to go to an area where a boss pokemon is daily to gain EXP / loot.
3. When pixelmon 3.0 comes out, add custom trainers around the map to make the game feel authentic
(Maybe even team rocket
)
Those are my ideas right now