The aluminum bulkheads are less flexible and will hold up better over time.
The floating battery strap system allows for more equal flex in the chassis. It also removes a place that the chassis can get tweaked.
The aluminum shocks are more durable than plastic.
The springs that come with the black kit are better springs.
You get front and rear sway bars. A performance item that almost all racers use.
The aluminum layshaft and spool are more durable.