You have a conundrum.
The BV350 is a very nice Scooter but double the money of the Sym Evo. New GTS or new BV350? BV350.
If the warranty will transfer and there is nearby Dealer support, the Sym would be tempting.
If the price on the Sym is negotiable, negotiate with this Cycletrader info...
There are new HD200's left over for less than the Evo which would be good ammo for negotiation.
Unknown resale value on the Sym but if bought right you could ride free for a period of time.
You already have Vintage Cool with the other Vespas, something the GTS doesn't have.