If you are going to upgrade just to get DDR4 it's not worth it.
If you are building new then DDR4 is worth it. In the future you'll have DDR4 which will be supported by current boards. Once the next gen AMD stuff is released later this year that supports DDR4, DDR3 will see a huge decline.
Price wise DDR4 is pretty much the same, speed wise it is faster so improves system performance slightly, so for a whole new system yes it's worth it.
If you currently have DDR3, and need to replace a part or repair and are on a limited budget, it's fine to get a current AMD system and maintain your DDR3. You can get quite a bit of system for little money compared to Skylake and not have to purchase new RAM.