I think a full evaluation will help us to see what his strenghs and weaknesses are academically and socially. I also think the evaluation may help us understand why the way he is and determine how to communicate with him in a way that he would not challenge our authority.
For us, the most interesting thing we learned about DS7 (other than his FSIQ and GAI were much higher than we were expecting) was how he tested on working memory (high) and processing speed (average). The processing speed in particular has manifested itself over the last year in his fluency (which lags behind his comprehension and reasoning abilities). He has noticed, for instance, that he is a very slow and careful writer compared to others his age. That may not be solely because of processing speed, but it's likely a contributing factor.
He took the assessment as an admission requirement to a local gifted school, so we weren't really in the situation you are in where we have to ponder what the value would be. But it has definitely been valuable well beyond.