The flaw in that plan is that Stock Car racing isn't a 'local sport' and is very much a 'travelling circus'. There are fans in all areas, but the bulk of the fans at Northampton on Saturday night would have been at Kings Lynn the previous Saturday, and will probably be at Scunthorpe next Saturday.
I would hazard a guess that on average, only about 10% of the crowd at a stock car meeting live within 50 miles of the track. I do 35-40 meetings a season, but my nearest track is about 35 miles from my home, and most other tracks I visit are around 60-90 miles away, with others further still, such as Taunton at 220 miles, and St Day (Cornwall) and Cowdenbeath (Scotland) both just over 300 miles.
F1 stockcars still have a strong following in the North West due to past history, despite there no longer being any tracks up that way, so many fans at their meetings are travelling from North and West Yorkshire, Manchester and Lancashire.