Having the metadata embedded in a publicly-documented file format is indeed an advantage of switching to DNG. A wider range of applications can read/write to DNG, so you're freer to choose the right tool for the job than when you're fiddling with XMP colostomy files. Another gain is that your DNG contains an updated preview, so you can see or use the adjusted image in other applications.
A lot depends on how much ongoing work you to do the pictures after you first process them, and in what program. If you do the vast bulk of your adjustments and metadata entry via Bridge/Adobe Camera Raw when the pictures are still new, create the DNG, and back it up. Any adjustment/metadata from that point on is exposed as it's not backed up, but wouldn't be hard to recreate if ever needed.
If you continually add more adjustments and metadata to your images, using programs like Lightroom or Expression Media, then backup the DNG after its creation, so the image data is safeguarded, and backup your ongoing work by backing up the catalogue. While it's helpful to save metadata and embedded previews back to the working DNG, there's no point backing it up each time.
Going DNG doesn't mean trashing your NEFs. Some keep them online to keep the option of using raw converters such as Nikon Capture which fail to read DNGs. I back them up, so I've the image data backed up in another format, but I rarely if ever see them again. Others simply delete them.
Treat yourself to a copy of Peter Krogh's DAM Book which discusses these issues and many others at length.
John