I agree with you about hair. I didn't find any influence although I have my hair cut very often. I always wear short hairs and I do have my hair cut much more frequently than my friends who keep long hairs.
For pubic hair, I didn't shave or trim it before 35, and I feel it didn't change at length for years. Once I began to shave or trim it, I found it seemed to grow faster. I'm not sure if it is because pubic hair will grow very slow or even stop growing when it reaches a length.