I have been highlighting for years. But my hair grows so fast that it is costing me a fortune to keep my snow white roots covered.
But if I let my roots go longer than 4 weeks -- which is pushing it -- my hair would start to look like Friar Tuck's tonsure. (My hair is so white, if I let it grow in very far, from a distance, it looks like scalp.)
Lately, I have been having the highlights brought up lighter and lighter so we will see where that goes. I bet I will have to always have some dimension with a darker color though or my face would just fade away.
Here is an article I found which shows transitioning steps that worked.
How to Go Gray - Tips for Transitioning to Gray Hair