From the dozen Hack and Tells (http://hackandtell.org/) held around the world to the hundreds of stories developers have of their first time looking at ffmpeg's source to the growing number of live Javascript console demos (great one here: http://www.youtube.com/watch?v=jArKzo-h3R0) to Dan Kaminsky's DNS bug discovery - I feel developers are very clearly capable of being impressed. It is a pretty regular thing.
It is, I will say, a very, very hard thing to do. I encounter it each day in my gig serving developer communities at Twilio. I have to bring my best work to them every time I ask for their attention - anything less ends in derision or, even worse, dismissal. Developers are natural skeptics whose daily work's default state is broken. This engenders a very high velocity needed to escape that skepticism.
Further, while HN certainly qualifies as a representative set, it is a specific demo of developer. There is a wide swath of developers who don't participate in this forum - poor reception here rarely means poor reception everywhere developers live.
Finally, I would submit that if impressing developers is one's goal in a project, one is probably set up for disappointment from the start. Amazement is an extrinsic factor that makes a poor primary goal as many factors governing success lie outsides the code one writes or the product one is building.
I always feel happiest when I fix the problems I want to solve elegantly and those solutions are widely adopted by the people primarily suffering from those problems. Whatever people think outside that scope doesn't really affect that satisfaction.