I love my car, but I honestly don't think that a Boxster is "exotic" enough to make people want to screw it up just for the sake of screwing/vandalizing some "nice" car.
There are people out there who will vandalize a car for literally no reason, other than they are jealous, but I bet a far greater percentage of auto vandalisms are tied to some kind of "incident" or motive directed more at the driver than the car.
Maybe it's a racial thing and you are of a nationality that some ignorant person hates - maybe you inadvertently cut someone off - maybe you parked in a spot that someone thinks is "theirs"...etc etc...
to think that just by parking my car in front of Costco, or the mall, etc..that someone will walk by a key it for no reason - I kind of think that is rare. maybe leaving the top down would encourage teenagers to spit in it, or someone to lean in and try to rummage through the car....but just sitting thee, top up, I don't think the car is tye type to "invite" vandalism.
to the person who got their top messed with - i have had two convertibles, a miata years ago, and now the Porsche. I used to NEVER lock my miata. i woudl leave the doors unlocked on purpose - someone once told me that if you have a convertible and somene is going to break in to rummage through your glove box or ashtray (for change) just leave it unlocked, they can take your change and they won't cut the top. cutting the top up will cost you thousands and at the very least a deductibble... my miata was "burglarized" once and I lost a few bucks in change from my coin holder - but no one ever stole CDs, the radio and ai left it unlocked everywhere for year...i drove that car a good 50k miles before i got rid of it...
although I have never left the porsche unlocked..
i have however left it wtih the top down when I know I will be "right back" and the weather is nice out and there are no trees overhead that might drip sap, bird poops, etc...