I would agree it depends on the kid and the school. My daughter did benefit, her private schools were excellent, she benefited from the small class sizes, the more tailored tuition and the pastoral care also, the schools were very hands on motivational and caring, with a
very individualistic approach, thr teachers were excellent, driven, supportive and highly motivated.
However it's not the same for all private schools. Indeed some are not as good as some state schools.
Just like you get a range of state schools, from outstanding to in special measures, you get a range of private schools also. The difference is the private schools tend to focus on different things to differentiate themselves, so you get the schools who focus on pastoral care, kids who don't perform so well and wouldn't get into the highly selective ones, through to those which are highly selective and hot houses, or those who focus on over seas students and their needs.. And everything in between, So it's different from state. They don't all aim for the same goal.. They go after specific demographics, and you need to pick what's right for your kid. Just like state.
So the answer to is it worth it is yes it can be, if you pick the right school for your child, if you don't, and you could have got the same or better from a state school, then no it's not.