I've been happy with using just one shampoo and one conditioner, but many longhairs seem to prefer using different products in rotation. What are the benefits of doing this? Can hair get "bored" of using same products all the time?

Rotating can be beneficial if the product you are using is building up on the hair.  Changing products might clarify or remove the build up.  If you are already using products that don't have -cones or other ingredients that attach themselves to the hair, then you would not need to change products.  Adding a clarifying rinse such as vinegar/water will also eliminate the need to change products.