Unlike most of HN (it seems), I like hearing from recruiters, because despite the very low signal-to-noise ratio, there's always that remote chance that one of them could be able to set me up with a "dream job". It's zero cost to me to politely reply to a recruiter and ask for more info, and I try to at least respond to everyone. What I've found is that they must have a lot of candidates they're juggling because fall…
If the email shows any effort whatsoever, mentioning a project I worked on, mentioning my current job, pointing out the role in question would fit my skills and it actually does, basically anything at all that suggests it's not just a form email sent to hundreds of people, then I will reply.
However, there's a third type of recruiting email that shows the person on the other side really is directly targeting you. It usually comes from the person who would be your manager, or at least someone who has a direct stake in the company (say the CTO or CEO at a small company). These emails I take seriously and appreciate. One of these led me to my current job.
Oh and I don't appreciate recruiting emails that have tracking links in them. Usually I will politely respond that I don't appreciate the tracking.