Joe,
Sorry to hear that you had a fire. The problem is, there should never be a spark in the intake system/circuit to start a fire. I am not sure how a bad plug could cause the spark to get into the intake system. You need to make sure you are not using a filter oil that will not promote the fire as well, as some oils have a much lower flash point
Do not condemn the use of the better filter because of the fire you had. The K&N as well as other paper media filters burn just as easily as they are also a consumable material; cotton/paper which then catches the rubber on fire and leaves a sticky goo all over too.
As far as your fellow racer having a fire occur in the filters during a race tells me he probably broke a cam and with the intake valves stuck open they are going to burn. That could have happened with either filter.
In almost 20 years, I have personally never had a filter fire, but have seen my share. Most of the time the fire is caused by an underlying issue, something allowing the spark/fire into the intake circuit. The filter fire was a result of that issue and not the cause of the fire, and is still the best type of filter you can use on your Legend car.
Randy - RPM