I've understood that there is no "native" way to automatically import stuff from a given folder in the Mac version of Evernote, without resorting to AppleScripts that may or may not work after an update to either the operating system or Evernote.
But, in the Windows version you can do this from Evernote itself.
So this is something of a workaround, but if you use Dropbox or any other Cloud storage service (who doesn't these days?) AND you have access to a Windows computer that stays on most of the time, like a media sharing machine at home, your computer at work, in the basement or whatever, you can set up Evernote for Windows on that one, and set the Import folder to be a folder in your Cloud service.
This way, any file that is placed in this folder from any computer, will be synced to Evernote through the Windows machine automatically no matter where you happen to be when putting it in there.
The caveat is that the Windows machine must stay powered on at all times for this to work seamlessly.
If you just want to be sure that the contents gets into Evernote eventually, you can rely on it being imported when you power on the Windows machine, anyway.
Just a clumsy workaround for something that should be implemented on all versions of Evernote!