Neil, I have looked at your inspection sheet and I am attaching a link to it for your review (copy and paste to browser) http://bit.ly/1vPZKRM I see that your air filter was marked as yellow and just shows slightly dirty. This can be the case after a short time. The tire depth and wipers are also just barely in the yellow range, marked just to make a note it will need future attention. I would say it is not cause for concern at this time as there were other needed repairs to your car.
The photo on the sheet shows the possible leak around the pressure switch and alternator belt & power steering belts are cracked. Both of these things are marked in red and more urgent. We did do a full inspection since it had been 4 years since we had seen this car. We want to make sure that you are informed of all the things that are in good shape as well as the things that are needed in the future and the things that are more urgent to allow you to make informed choices on your Miata. Thank you Neil for your feedback and please let us know if there are any other questions or needed repairs. Christine Henderson