Interesting timeline for Martinsville. They stared with 750 seats but the timeline through 03 shows massive growth especially in the last 10 years.
http://www.martinsvillespeedway.com/track%5Finfo/track%5Ftimeline/
Iif you watch the replays of the old (pre-1995, or so) Cup events, it's cool to see the relative lack of stands (compared to today) at places like Bristol, Daytona, and Richmond.
Check out Dale Jr.'s show "Back In The Day," on Speed Channel if you're into this kind of thing.