As one of the 10 abarth specialists at dealership level, I can confirm that yes the assetto and essesse kits are dealer fit upgrade kits. they must be carried out within 12 months and 20,000km of registration and are carried out at dealership by technitians trained in turin by abarth. you can only upgrade the car ONCE, you cannot do the two kits at different stages and the esseesse kit must be acompanied by the assetto. upgrade kits will have a 2 year abarth warranty from time of fit.
the abarth grande punto has an OTR price of £13,500 and an average lead time of approx 4-6 weeks (dependant on exact specification)
I would strongly advise that you contact your nearest dealer for further details as speculation simply makes our job harder.
i am based in glasgow, you can find dealer locations through the fiat website or http://abarthuk.com/category/uk-abarth-dealers/
also www.abarthcars.co.uk is the official abarth website
if you need more info contact me on d_murphy@arnoldclark.co.uk