I have over 22000 miles on the GTS and have gone through 5 rear and 2-3 front sets of Pirelli GT 23/24 tires and more recently a set of front and rear Pirelli Diablo tires. I had no complaints in the wet or dry handling with any of the previous tires.
I seem to get not more than 3400-3500 miles on a rear tire, with not quite doubling the miles on the front tires.
It seemed as I approached 22,000 miles this riding season I needed a new front/rear tires (I also needed to replace the rear swing arm bearing). I chose to try the newer Pirelli Angel Scooter tires w/ a matched set front and rear. They were even less expensive than going for another set of Diablo's. I feel compelled to share the experience. These tires felt different, right out of the gate. With now 4 weekends and 400+ miles of riding, I have to say these are great handling tires. I feel as if I am "velcro'ed" to the pavement and have much less Vespa "wobble". Both wet and dry they feel unlike any other of the other Pirelli tires I've ridden on.
My supporting anecdotes are 1.) that the tire feels so soft and grippy that I found myself continually wanting to do bob and weave moves on smooth straight-away's just for fun, long after I wore off the "chicken strips" and 2.) The grippy sensation made me feel the need to check the tire pressure to see if it had somehow lowered, (I tend to keep my rear tires nearer 35-37 psi in case I ride 2 up), the pressure never moved in 400 miles, and 3.) the grippy feel has evidently let me corner harder than my usual conservative riding and I have scraped underside parts (riding 1-up) off both left and right turns twice each, somewhat unexpectedly in those 400 miles. While I don't recommend or endorse scraping underside parts on turns... I'm just saying and reporting... I must have felt more than usual lean confidence.
I'm only curious to know if they last as long as the previous tires - I'll let you know