Chris, it's usually recommended to scrape down to get rid of vegetation that might later decompose, but for our particular roadbed it's not really needed. I scalped the roadway with the mower and it has also had some compaction from our own traffic in and out of the place, so it was not like it had a lot of grass on it in the first place.
I would suggest that for your future road even with the clay the cloth may be an economical addition to ensure stability.