We don't have full details yet but the listings mention an improved frontlight and touchscreen, a whiter screen (described as "all-new paperwhite display"), a faster CPU, and a number of new software features. This ereader is expected to ship by the end of the month.
The 2013 KPW is going to get Goodreads integration, new parental controls, a vocabulary builder, and new navigation options.
It doesn't appear that the parental controls will be available at launch but when it is released in an update it will let parents restrict what kids can do on the ereader similar to what Kindle Freetime can do with the Kindle Fire. The Goodreads integration will let you be more social in your reading, and the new vocabulary builder will help you with studying and learning.
All in all this strikes me as an
incremental improvement to the existing ereader and not really a new device. This is similar to the way that the Kobo Aura is an improved and updated Kobo Glo.
Update: After re-reading the listing I have changed my mind. We could be looking at a next generation screen on the 2013 KPW, and that is more than an incremental improvement.
Both new ereaders have improved hardware and new software features, but that might not be enough to justify replacing your current ereader. If nothing else Amazon has a history of releasing updates for older Kindle models. The 2011 era Kindle Touch, for example, received an update only last month.