H.W.
Woo-hoo! You are in luck because I have nothing but encouragement for you.
Our son has some attention issues. He was given an evaluation in the manner similar to what you describe, a Woodcock Johnson test along with a few other more specific tests to address key issues. What we discovered was that, despite his lack of fluency-- which makes him appear slower-- he's very intelligent. Being able to take this information to the school and share it with teachers and the other educational professionals has been so helpful. Knowing that he is as bright as he is can help me to advocate for him, while knowing his challenges can help me work harder to give him good information and resources.
A diagnosis won't signify who your son is, however it can help you get more for him. I don't know if your son is sensitive to tests-- mine was 'fine' doing the 3 hours eval. (I put *fin*e in quotes because we asked how he was, fearing he'd be wiped). If it were me, and I knew the doc was good-- I'd do it, with either a hotel on one end or the other. To us, the results were a revelation and a validation... it will help us so much in helping our son.