Test drive or not is typically either a set policy of the dealer, or at the whim of the salesman. I live in Orange, Cal, and half the time you can't tell the millionaires from homeless, so most dealers don't give you a lot of trouble unless that light goes off in their head that says you aren't buying. I've driven all kinds of cars, and only a couple were a PITA to get a test drive, the worst was actually a stinkin Nissan dealer.
With something like the Viper you have to understand the dealer doesn't WANT to sell it until the end of the year since they only get one, and its really to bring people in so they can sell them a minivan. When I bought my last Porsche the dealer was crawling with high school kids that really were getting a Porsche for their birthday, good grades etc.
The main thing with a car dealer is that either they will let you or they won't, you can't hang around and "talk them into it". Don't expect to drive cars off the showroom floor, or buried six cars deep next to a building (My failed attempt in 1974 to drive a Pantera). Find a car on the line you like, ask for a test drive, and if you aren't behind the wheel in 10 minutes go to another dealer.
BTW a good story goes a long way, ie my grandma is buying me any car I want for my 18th birthday, etc.
All that said, don't waste all your money on a fast car and insurance, you aren't going to get to drive it fast anyway.