Did you use the trade yield modifier already in the XML for the +2 commerce per trade route trait?
That actually works as a percent of each trade route, not a total, so currently setting it at just 2 is kinda useless. (You'd need to have a singe trade route producing 50 commerce just to get one more commerce).
I find setting it to 25 (aka 25%) to be balanced, so for every 4 commerce each trade route makes (not the total trade commerce added together) you get 1 more.