I have been lucky to get Wagyu cheap enough (relatively speaking) to buy and cook it quite a few times. My $0.02... It is almost worth the investment in [less expensive] Wagyu when cooking things like beef tenderloin or filet. As for brisket, or fatty steak cuts like ribeye, I do not find it to be worth the money. I have done both. Don't get me wrong, the Wagyu brisket I have done is probably the best I have ever had. I guess if I had an endless supply of cash and/or free meat I would see it as worth every penny. The biggest probelm with Wagyu brisket IMO is that while it creates a textural improvement, the smoke, the rub and even the process of rendering minimizes the relative improvement over a well marbled choice or prime.
I do have a single piece of Wagyu in my freezer waiting on a special occasion. It is a beautiful tri-tip. I got a few when I bought it, and did the others to a light medium (Wagyu does do better cooked a little further than cheaper cuts of beef I think). My intention has been to use the last one for a trisket, but I haven't been able to bring myself to it just yet.