The worth of upgrading to P12 depends on where you are now and the hardware you're running. Poser 12 added significant hardware support with support for Optix and RTX GPU's. The render speed improvement is exponential if you're using an RTX video card. Easily 10 times faster. Even CPU rendering saw significant improvements with the addition of adaptive sampling. There is a downside to P12. With the end of life of Python 2 we were forced to migrate to Python 3. Some older Python script aren't forwards compatible.Poser 12 also removes the Face Room. Some of the technical limitations of the face room were hampering future figure development. Single skin or "Unimesh" figures aren't compatible with it's technology.

And that's just the difference from Poser 11 to 12.

The exact release date for P13 is not set yet. There will be upgrade paths but none of that's been set.