I've been on two meager rides (~60 miles total) without scratchers and haven't seen the temp gauge go above 4 bars (basically it stays the same after warm up). This is riding on mostly hardpack snow for a ~3 miles before hitting anything halfway decent. And even then it was mostly trail riding on old snow with the intermittent breaking new trail or finding powder stash ride.
I suppose if you are always riding in crappy snow they might be necessary, but otherwise it seems to be a nice-to-have just in case it gets crappy. I also have a 2010 XP that didn't have scratchers until this year. I finally had it overheat once last season on a cross country trip where there was a stretch of highway we had to traverse followed by really low snow (i.e. basically no snow). I installed the carbide cable scratcher and it looked like it was jacked up at the end of the first ride, but I was in a hurry putting the sled up and didn't check real close. For the riding I do I'm not sure they are worth it.