I just tried it myself, worked like a charm! I had to create a POI first, then did as you describe.
I also just created my first POI category "Junkyards". No I might do the custom ICON that you mention, but obviously, fairly complicated for minimal gain.
Also, what was the source of this information? How up to date is it, and can I keep it up to date? I know in the north east with all the construction, frequently they are moved/removed/closed.
Glad it worked for you! The source of the information was from poi-factory.com (search on "rest area", there is a rest area combined file. I started with that file, but tweaked it quite a bit for the Avic. Basically I put it into excel and edited a bunch of the lines to standardize the format and output. The results of the standardized output is what is in the Excel file.
According to the poi-factory site, it is up to date as of 8/18/2009, but I am not sure if that means there were just additions of new locations or a few corrections. Basically, it seems this info is contributed by poi-factory members, and not an official government list of rest areas, so with no one driving to all of them, it will be difficult to verify. It was on the mark for my road trip.
Keeping it up to date isn't as simple as downloading the file from the site, since I tweaked it quite a bit. I will be looking every now and then for updates, and will post changes as I see them, but I will admit I won't be actively looking until my next road trip. If you see an update, get in touch with me and I can do the tweaks (I have it automated in Excel) , and post the file.
However, you can add new Rest Areas right in the Avic (without all the extra info, just the location), then download the file, make the changes in notepad to add the info you would like to add, and upload it to the Avic again.
Hope that helps!