Worth it? Absolutely. For one, it's much more stable.
Replicator is an excellent addition, especially if you spend any time creating patterns and textures for backgrounds and lower thirds.
3D filter is great for creating 3D perspective in objects, and there are also new filters for downloading when you register.
Float space is important if you're working in HD or film or want to get the most accurate image processing.
Some nice enhancements to keyframing, particles, working with the motion path behavior, autosaving, and the ability to control the size of an image by fixing its resolution (which can be useful when trying to avoid the 2K size limit).
Better integration with other apps (FCS and also iTunes and iPhoto).