First, from your post, it seems you are already working with a particualr instructor. For me to change instructors, I would have to be in some way disastisfied with my current instructor. Also, there would have to be a significant improvement in the teachign skill, goddness-of-fit between myself and the next instructor. I wouldn't change just based on rank.
Rank denotes a certain level of expereince (which is important). It even tends to denote a certain skillset in actual tecniques. It does not equate as well to teaching ability. Personality. Leadership. The sorts of things that may lead me to be a better practitioner. It doesn't denote valid experience outside the given art of rank. For example, I'm almost 2nd dan in TKd. That does not take into account 8 years of Aikido training, several years of traditional karate training, wreslting expereince, wing chun expereince...basically, training since I was a kid in a myriad of arts. It doesn't take into count my professional background and other teaching experience.
I like my current instructor and am happy at my school. It's not perfect, and I am well aware of where certain things could be better. What do I do? I cross train when I can. I network and do seminars with high ranked intructors to pick up things that I might not get in my day to day training. Honestly, whiel that's all well and good...at this level, it's all about me and how m,uch I'm willing to grind through extra practice, conditioniing and working the basics over and over and over again. NO magic special techniques...no secrets.
Doesn't take a 10th dan to get me to do that.
Peace,
Erik