I've noticed the same thing. I suspect that there are tons of people from the NES generation who already collected the NES and games, since that was what the majority had when they were kids. Perhaps some of them are looking to experience what they missed on the SMS.
The recent hype about 3D TV may have also sparked some interest in the SMS 3D shutter glasses and games, since this year's CES was pushing updated versions of the same technology.
On one hand, it's good to see the SMS get some love. On the other hand, it's a lot more expensive adding to my collection