Average American Net Worth = $301,000
Average New car cost = $32,000
I'd say that 10% number is hit a lot more than you think (though likely with a lease). Pretty much by anyone driving around in anything nicer than a new Civic could be above that threshold.
I'm not saying it's smart, but I'd bet there are quite a few 918 owners with less than $100 million in net worth. The average Ultra High Net Worth person ($30 to $80 million) has $20 million tied up in business, $5 million in real estate, and $5 million to play with. (Financial Times study)
Again, maybe not smart, but but I'd say that's your target market: People with $5 million to play with. Some will play the market, some will play with cars.
http://www.ft.com/intl/cms/s/0/dfb64bdc-4d55-11e3-a220-00144feabdc0.html?siteedition=intl#axzz2lmSgY6eN
(edited with the correct link)