There have been many posts on many forums about Iridium Plugs and if they are worth the extra cost.
I personally fit them to every bike I own as I have only found proven clear benefits using them, especially in the Z1300 with its prehistoric ignition system.!
The benefits I have found with the 1300 are :-
Improved easier Starting.
Smoother and more stable idle.
Better all round performance
They also last more than twice the mileage of regular plugs and never need gapping, so the extra cost is covered in reality.
If you have not tried them, then I suggest you do as I am sure you will be impressed.
The video below shows some pretty solid proof they are superior
Keep in mind, on our bikes (and others that utilize dual fire coils), half the plugs are 'firing' backwards; that is: firing from the 'ground electrode' (it's not a 'ground' on a dual output coil circuit) to the centre electrode of the plug. Not sure how much the iridium centre electrode is a benefit under those conditions. Whenever I pull the spark plugs (I have iridium plugs), I always re-install them in their opposite coil partner's position (never noticed any difference though).
Getting on board with this experiment. The bike is very responsive, pretty much not needing ANY choke to start, crisp at the throttle as a crisp can be. These plugs will be arriving soon as I place the order - any treat the bike needs... NGK BPR5EIX - >>>>> the engine blows up I'll be hunting you Phil! haha