In my book higher performancing tyres are always worth it. They're the only thing connecting you to the road. For instance, even though I enjoy driving my car, the traction light extremely rarely comes on, the tyres are that good even in the wet, even playing. Much better than the GS-D3's. Don't get me started on the RE040's.
Pirelli Zero's are good, but having had then on different vehicles, not that fussed, plus it's a steal item, well it is here as they're more expensive than the Yoko's.
What do they rush you for a set of Michelin's (Pilot's I'm presuming) over there?
That may have some bearing. Ultimately the firmer the sidewall is the better the cornering.
Whatever you go with, put the same thing all round Rob.
Where are all the tyre sponsors when we need them????