You've proved my point. Speedway (and the others you mentioned) were not viable, hence they chose to redevelop the site. Wimbledon previously closed in 1991 for exactly the same reason. And both 1991 and 2005 were periods when Speedway was in better shape than it is now!
There is absolutely NO chance of Wimbledon, Coventry, Swindon, or any other closed tracks being revived and the sooner these campaigners open their eyes and get on with their lives, tbe better. Everyone is getting excited about Buxton - that won't last the season for exactly the same reason.
Speedway. Is. Not. Viable.