Ron wants to know if it's worth the money buying a 4K Blu-ray player. Leo says only if he's planning on buying a 4K TV and only if he's planning on getting one over 55" in size. Then he'll want not only a UHD Blu-ray player, but also a 4K TV that supports HDR.
The other issue is content. 4K HDR Blu-ray titles aren't widespread. His AV Receiver will also need to be upgraded to handle 4K as will his streaming devices. It's a cascade effect of upgrading components, so he shouldn't do it unless he's willing to get that 4K HDR TV. There's no 4K over the air or cable/satellite in 4K either. It's all streaming and optical.