Plastic engine skid plate
 

Do people keep these on? Is there any benignity to refitting the under engine plastic skid plate as it currently off whilst I sort my rad

Some do some don't , keeps all the **** out but also keep heat in :)

Both mine are off the car

Mine is on, they must have been put on originally for a reason.

It must streamline air flow under the vehicle??

They do stop a lot of crap getting under the car, if you're driving it all year round in all weathers I'd suggest leaving it on. My sump is like new but when Rich had his classic sti the sump was in a real state as it had been removed at some point in the past.

My understanding is it does help with cooling (slightly) if you have a TMIC as is helps draw air through the scoop however having the exhaust and sump in fresh air pretty much balances it out, especially if you have a FMIC.

Also without one you will notice any minor leaks a lot sooner as the tray does not catch any drips!