My apologies in advance if the suggestion has come up already - have you tried going through all the suggestions here?
At the moment we have the frustrating situation of producing a large quantity of mana in most town/cities. Even using magic on a regular basis, you still end up with tons of the stuff!!
So I would like to make a suggestion which you may, or may not, think is a workable idea.
When the new trade becomes active, I would like to see the ability to 'trade' with the hubs using mana. The idea is fairly simple. The trade hub will 'buy' mana at a rate of say 1000 mana/1 gold (mana is easily produced hence the low price ratio suggestion). Likewise, as it is a trade centre after all, it will 'sell' mana at say 500/1 gold.
This would allow those who have excess mana to do something useful with it, and allow those who need it to have the facility to get some quickly. A further refinement would be that this is restricted to individual trade hubs - e.g. the hub can only sell the quantity of mana it has purchased from sellers.
Thanks for taking the time to consider this