Very perceptive for someone that knows nothing about speedway, the answer is indeed no ! 8 point lead is for the semi final only, the final starts all square. If Swindon progress (which they will barring any disasters) then they will be at home in the second leg of the final, not much of an advantage but at least finish at home.
We never seem to win the league but Wolves in the final will be very tricky over 2 legs.