I feel the income over time incentive is slowly stopping to work for the average player, as most of the people really have too much cash and little reason to spend it, thus an overall lack of traders.
So what is left is trying to steer those who actually need cash into all the activities evenly, not just getting them to focus on the most profitable one - which i think is currently group PVE, or ores ?
Maybe the solution would be to mix it up a little, though I'm not sure how much work it would be.
Basically make it a rotation where on any given day it's more profitable to mine, trade or PVE. This could probably most easily be set up with events such as those described in A plan for longevity
Alternatively, a more intriguing solution could be to tie the PVE Controller rewards to a global "rewards pool" (or maybe make it per House to encourage more focused interactions?) that gets filled with a percentage (or a multiplier would make more sense?) of the trading volume being done on the server. Basically, as more and more people PVE and not trade the liquidity for NPC bounties would dry up, nudging people to pick up mining and trading again as the more profitable option until the bounties cash pool is restored again.