I guess for the MOT they just look at the tread and the legal limits rather than the make of the tyres. I never let mine get anywhere near the limit. there is an interesting chart on the wall where I get my tyres showing how the stopping distance goes up as the tread depth goes down and it is quite eye opening. they also say that the Hankooks are at the top of the budget range so a good compromise if you cant afford the premium tyres.
I just always believe in putting the best tyres and brakes and any other parts, especially on something as quality as the Lexus, but also from a safely aspect. The same reason I put V power in, even though some on here say it doesn't need it and they don't notice any difference, I notice the change from the higher octane and the additives that keep it clean.
The multispokes are nice if they are in good nick and so far mine are fine and are so much nicer than the 5 spokes in my humble opinion. I still love the way the Mk 1 looks even after all this time and wheels can make or break the look.