These days, I'd say you HAVE to include the new VW's; there just aren't enough old Beetles on the road anymore to make the game really painful--I mean really fun.
I loved it when I was a missionary in South America for two years. They were still making the old-style Beetles in Brazil and Mexico in the early 1990s (and perhaps they still are?), so they were all over the place. You could really rack up the Slug Bug points quickly.
I went to school in So Cal, as of 93 they were still manufacturing bigs, and many people I knew, (surf nutts, and tree huggers from UCLA) went to Mexico to buy cars, because they held up.