Vespas are high quality scooters, but I don't know about parts, I'm used to bikes that I can get parts from online places like cheapcycleparts.com and bikebandit.com, and they don't carry Vespa parts. Once I have bought a bike, I don't like having to return to the dealer for anything. My local dealer has a red '08 S150 fresh out of the crate, for $3299 OTD. While $3299 may seem like a lot for an '08, it is new and that is OTD. OTD is usually $700-$800 above retail price. I had my eye on it, but wound up with my Zuma back. I've noticed a lot of the scooters on Craigslist have been dropped, and I would not be interested in one of those unless it was a dirt cheap beater just for transportation.
I won't spend more on a bike than I think it's worth, but if it's a good deal, I don't seem to have a problem buying bikes I don't need.
2002 Vulcan 750, 2013 Royal Enfield B5
2001 XT225, 2009 Genuine Stella
1980 Puch moped