It could be that the project posters aren't serious, or that they're not impressed by my credentials/portfolio, or maybe my higher price.
Does anyone in the HN community regularly bid on freelance projects and get them?
There are a number of other free or inexpensive things you can do to make yourself look better: use a sharp looking picture of yourself, have a halfways decent website (a one page site is OK - leaps and bounds better than nothing), email @yourdomain.com, toll free numbers are fairly inexpensive, sign up for a BBB membership, etc.
Also, I can't stress enough that you need to have good clear writing that touts whatever skills you have. (On your profile and your personal site.) Don't lie, but do brag a little. If you're not the best at copy-writing, have a friend look over it.
Also, make sure to mention which city you're in / near, as many buyers prefer to work with someone local.
It's OK to specify on your personal site that you only accept work through [XYZ freelance site].
A blog on your site is a bit more work, but can pay off in the long run. You won't get a lot of business directly through the blog, but it will help boost your google rankings which _will_ bring in business. Keep it strictly limited to informative articles on topics you're interested in working on, and try to post regularly - at least once a week to get started.
Lastly, you want some referrals from me, leave your info here: http://nfriedly.com/techblog/2010/12/calling-all-avaiable-we...
Oh, and what everybody else has said: raise your rates. Start at $45/hr and raise it by $5 every few months.
I include a few points that can help them clear up ambiguity in their project requirements, and generally offer an hour of project review as a complimentary service.
On this call (or meeting if they are close), you can quickly determine if they are just trying to get a free hour, or if they are genuinely interested in a more experienced consultant who can really help them with their project.
My experience is about 25% of posters will respond to such a bid/proposal. Of those 25%, about 33% are actually looking for assistance and open to paying for experience.
Notes: I moonlight, and usually bid on projects for which I estimate 40-120 hrs of work, and they are generally in the realm of system administration, database optimization, and php (often on shared hosting). Not the greatest client group with which to work, but you encounter some interesting challenges.