the parts bin is a great idea.
the dealer buying back from you, IMO, wouldnt work. there would be such a minefield to navigate with parts being classed as second hand, not under parts warranty etc.
it may work if fiat bought them back and classed them as reconditioned though i guess. i doubt its something they would ever entertain mind.
we kinda questioned the logic behind it when in italy, especially the fact that youd have to bring a luton with you to take home your parts, and we were simply told the customer owns those parts, it is part of their car whether fitted or not.
if it was me i would probably only ask for the handling kit box back, however i can see a few of the turbo's/manifolds and backboxes finding their way onto e-bay pretty soon, i would imagine they would be a useful source of spares for an abarth/t-jet enthusiast, plus im not sure what else the IMI turbo is used on outside the fiat range.