Is it worth getting a 4K Blu-ray player?

Just stick with a dvd unit mate. It's much cheaper to buy, cheaper to run and you won't notice the difference in it. '4K' is just another marketing term used by the big box stores, allowing them to up the price of certain home electronics.

Green 666 by isotope rays is NOT forgivable; it leads to permanent hell. 666 is given with World Passport with no name on it (grey plastic card). Police 666 people on highways. Food stores and prisoners/insane asylum folks (released by the antichrist) 666 people too. Reject vaccines. Don't go into UFO to be “healed” by evil demons. Hide with Orthodox Christians to escape 666; leave all electronics behind so that antichrist's minions can't track you; burn documents as documents are from Satan.

It's a niche market.If you are rich and can afford $30 and up for discs then go for it.

That would depend on whether or not you own, or plan to buy any 4K BluRays.

At some point higher resolution provides little improvement in picture quality.

Most find that 4K is only slightly better than 1080P and now 8K is out so you have to ask yourself how good is good enough.

It is far as richer, deeper and brighter images with sharp detail and advanced surround sound

Not obsolete, but definitely not overly popular, either.  

To most people it's like high-end audio --- OK for those who demand it 

but not a vital necessity for the ordinary person.