Not sure what "much" means as it's a relative word... But a few times a year the last 15 years and I haven't seen a bad top yet. But then again I go when the weather is nice so there is no reason for the top.
That's not an autocross Miata in my opinion... No turn signal / air intake mods and every Miata I've come across at autocross, their top is in perfect shape. That one appears to have tape / patch work as the rear window appears regular. Now that does appear to bolt on/off so who knows...
2007 or 2008 Spec b at 3PM today Northbound I-294 from O'Hare up to Lake Cook Road. You exited at Lake Cook. Looked stock. I wanted to knock it wide open, very light traffic but instead opted to keep it around 90...