Thanks ralph.m, and congrats on being staff member of the year!
I've made the app free just for today. I've heard elsewhere that there are a lot of people who use price-drop monitoring software and websites. So far, this seems to have backfired and killed my #4 app store (navigation) ranking in Australia, at least temporarily.
Both your suggestions are good. Having suffered app store rejection previously, I was pretty cautious about the description this time. I'll see if I can get some more aggressive marketing in there with the next update. Good advice.
The YouTube video is also a good idea, although I don't get many visits to my site: most people seem to prefer clicking on an app-store link rather than an unknown website. I'll see what Apple's policy is regarding linking to 3rd-party sites from the app metadata.
Thanks for your thoughtful and helpful suggestions so far. I've been a bit silly to assume that "if you build it, they will come".