Is upgrading from a Ryzen 7 9800X3D to a Ryzen 9 9950X3D worth it for work and gaming?

I wouldn’t spend that kind of money for a change you may not notice. Check your CPU utilization and benchmark the actual programs you use first. If your work regularly maxes out the 9800X3D, then the upgrade might make sense; otherwise, the performance gain is unlikely to justify replacing it.

The work side depends entirely on what applications you use. Video encoding, 3D rendering, compiling, and other heavily threaded tasks could benefit from the extra cores, while office apps and lighter work probably won’t. For gaming alone, keep the 9800X3D.

For gaming, probably not. The 9800X3D is already an excellent gaming CPU, and you may not be CPU-limited in the first place. In some games, a 9950X3D could even perform slightly worse. An upgrade within the same generation usually isn’t worth the money unless you specifically need more cores for demanding workloads.