Yeah - I think your right.

You should check your tyre pressures after a trackday anyway - you can loose some pressure through the valves at high speed. Your not supposed to use plastic valves on a racebike and metal ones should always have an o-ring seal.

That's correct. I use metal caps with a seal. The cap is the primary pressure retention device, NOT the valve core.

My tyres don;t deflate on trackdays and even if they did I'm not bothered as I stick the bike on the trailer to get it home.