Here is a list of new features with v14 http://www.nuance.com/products/help/dragon/dragon-for-pc/enx/professionalgroup/main/Content/WhatsNew/new_v14.htm. Nuance does not claim v14 to be more accurate than v13 for everyday speech to text functions. So, it may not be worth paying for the upgrade unless you want the new features. They don't seem all that impressive for the extra money.
Some of the new features include,
- auto-text commands
- windows 10 & office 2016 support
- improved transcription accuracy for recorded sources (not live)