Picked up an '06 Viper roadster six months ago and it is my DD replacement for the '01 Z06. The Viper makes the Z06 feel like a luxury car. The Viper is more of a raw sports car than the Z06. These are not a complaints, just observations. However, that is what makes a Viper a Viper and I enjoy driving it every day. You will not regret it, and furthermore, Vipers are more exclusive than Corvettes. I see a bunch of C5 and C6's but have only seen 4 Vipers where I live...and it's fun to watch people pull up and point, take pictures, etc. That never happened to me when I owned the Z06.
It's funny you mention how rare they are. I had never seen one in the road since I moved here until today it was a gen4 in graphite metallic. Not my color choice but it looked sooo gooood. I have seen a couple in the show room of some dealerships but seeing it on the move it's a completely different experience.