They become part of your pria record when you complete the 8710 so employers WILL see them and the scores you got, but this is after you have been offered a job. It reflects your motivation so I would do your best as with anything in your training.
Check rides do matter, even more so after Colgan. Some airlines won't even look at you if you have so many. I personally have two and in the 121 airliners I've gone to both they just asked what happened. I took responsibility and we moved on but I have a friend with 6 busts and he is not even getting calls from anyone with ATP mins plus a ton more.
As far as your instrument rating goes, the big thing I say is RELAX and dont stress yourself out. The only reason you are going on your check ride is because your instructor thinks your ready. This is a big thing ice noticed with my students and as soon as they relax the check ride goes by like nothing.