if you want to hang up there at FL380, pretending your a jet...good for you. Personaly I will fly whatever the boss want's me to fly, even if it doesn't make sense. That said, I would take a ragged out Citation ISP at 29000ft from SEA to MIA for an even million, before I would drop 5 mil on a Piaggio. At 355 kts it might be a horse race to Florida, but I keep 4 mil in my pocket...
I rarely read such useless crap. First of all if you want to compare those 2 aircrafts you should compare same TT prices. Anyway it's not only the price that matters but mainly the cost (depreciation, interests) and the reselling potential/demand.
Technically you obviously don't have any clue on how this aircraft performs and how it actually saves a lot of fuel compared to any jet. Just try to compare perfomances and DOC on a 1000 NM trip in ISA + 20 conditions (if these words does have a meaning for you).