Ok, so I came up with this great idea to make these more tolerable.

First off convoy missions right now are 35 coupons, and from 1 plunder you get 35 coupons + 15 you stole = 50. But having to wait for that SS is painful.

IF the convoy mission (still one) was 50 coupons, and from one plunder you would get 50 coupons + 15 you stole = 75 it would be much better, with a maximum of 2 plunders per day instead of 3. With the amount gained being the same, 150 coupons.

This way you make everyone happy, the plunderer waits for 2 SS instead of 3, and the convoyer gets more coupons but not too much.