I never heard of putting coulters on a disk. But I guess anything that slices and dices should help. My concern would be taking weight off the discs, but yours is pretty heavy. Let us know how it works.
I think that the additional six coulters did an amazing job of chopping up the ground, and the only issue I ran into is that some of the brackets that secure the coulters to the 3"x3"x3/8" cross members moved a bit due to side loading. I'm going to add stops either side of those brackets to prevent that from happening again. Other than that I see no reason to remove the coulters.
I paid $1,150 for this disc harrow around three years ago, and compared to new hydraulic disc harrows from Land Pride and similar which cost $10k to $15k, this one is pretty darn good. No doubt a new harrow would be as tight as a drum and be easier and nicer to work with, and probably do a better job. But for 1/10th the cost and 80% as good a job it's money well spent.
I do plan on some more upgrades, some more pressing than others. Here are my ideas in order of importance.
1. Weld stops on cross members to prevent coulter brackets from moving
2. Eliminate or reduce play in tongue
3. Replace tongue jack
4. Add hydraulic cylinders to control front and rear disc gangs
5. Add hydraulic cylinder to control tongue angle
6. Replace discs on front and rear gangs