1st idea:
I always figured would be cool if the base got a bonus from merchants also. Merchants are in turn traders so maybe a 5% bonus for each merchant in legion. They should be like Miners giving mineral production bonus or the Vygoid for research. Why is the trade bonus limited to just Trade pacts?

2nd idea:
Merchants time between shipments maybe be cut in half or something? Merchants are traders. Waiting 3 mins instead of 5 would give people reasons to want to be merchants.