I am considering to couple the incentives to the trade volume of a pair. For example, every three months, we would measure the trade volume for wUSDC.b or wUSDC for the past three months, and adjust the incentives accordingly. More trade volume results in more fees for dexie, so incentivizing a high-volume pair more would make sense.
However, more incentives will likely lead to more volume as well, so incentivizing a low-volume pair actually has its advantages too.
Combined Swap for CAT-CAT pairs may solve this problem, as it would be able to combine a path from both order books, such as wUSDC.b->XCH->wUSDC.
Overall, liquidity plays a role here too. A 5% spread for an XCH/stablecoin pair traded on an external liquid marketplace is different from a CAT/XCH pair mainly traded on dexie, such as DBX/XCH or SBX/XCH. If we incentivize liquidity up to a 10% spread, users will experience higher slippage.
If the 5% spread is an issue for DBX and SBX, then I would rather increase it for those pairs but use a lower spread for XCH/stablecoin.