HN will generate similar traffic to a techcrunch post, if you look at the raw numbers. The big difference is that the TechCrunch traffic is from a readship of a million, and those who click are genuinely interested in your service, that they just read about.
HN will also give you a pretty large boost of traffic, but more are just interested in checking you as a startup, not as an end-user.
3-4 years ago (first time I had a project covered by TC) it delivered ~3x more traffic compared to what I see nowadays (probably because the volume of daily posts has skyrocketed over those years).
I'm sure controversial topics (Angelgate, etc) still drive traffic, but if HN is creating 10k uniques for top stories then the "HN effect" is greater than what average TC coverage provides.
Plus, I've seen a lot of early adopters and tastemakers have moved to HN for finding things more on the cutting edge.
As much as I hate to say it, planning an effective HN marketing campaign may end up being more useful than trying to pitch the bloggers...