I just got my LC back from its 5 year service but have only done 17K miles from new. I have the 20 inch wheels and the Turanza tyres are worn to an overall average of about 5mm tread depth left.
Interestingly, the fronts are pretty evenly worn across the width of the tread but the rears are worn about one mm more in the centre than the edges of the tread. This usually indicates over inflation but I have always set my pressures with a Snap-On gauge to the recommended 2.3 bar and this is confirmed by the on-board system.
On the way back from Hedge End, I noticed that the car felt "floaty" so I checked the pressures the next morning and found that they were about 2.5 bar all round. I reset these to 2.3 bar and the car feels OK again.
Regarding replacement tyres, I wouldn't be too concerned about getting run-flat ones. I had an Aston DB9 which was fitted with Bridgestone Run Flats as standard. I changed these for Michelin PSS and the ride improvement was huge.
Has anyone who has put new tyres on their LC got any comments?