i think head and tune would be best bang for your buck then the lightweight hood looks good. I'm running the adapt primary on my 18 without the starter ring and it seems to work well.
Terra Alps billet head with proper dome design and compression can gain good power, especially if your riding high elevations.
ECM tune from Terra Alps 7 hp gain and reliability
Muffler 3hp gain
Pipe & Y pipe up to 10 hp depending how its tuned.
Cylinder Porting good gains
870 big bore kit 22% gain on pump gas, most powerful kits available.
These performance packages keep the sled fun with great throttle response and acceleration with no lag like a turbo and there headaches.