I really think it depends on the schools you have available to you. DH and I went to boarding schools - I loved it, he didn't. I wouldn't have played as much sport or music possibly, but my results weren't stellar and a local state would have sufficed I'm sure. My world view was very narrow at 18 - I didn't know anyone at state school and thought everyone had big houses, ponies and tennis courts.
Our four children have all been through (superselective) state grammars - one is at Cambridge, one at another excellent RG and the younger two still there. Many of the things people are citing are offered at their school - they are one of the best (state) cricketing schools in the country, have matches against the big local indies, a strong fencing team, have sports tours to Dubai, Argentina etc, trips to NASA, MUNGA, have amazing sport and drama opportunities - and have an enviable conversion rate of Oxbridge application to offer ratios (superior to several well known public schools near here, acc to recently published data in the Telegraph).
I did feel guilty for ages that they weren't at private school - DS1 won a top scholarship to a prep school and whilst we were agonising over what to do, my parents advised against getting on the fees treadmill if we didn't have to...!
Research carefully what you are paying for and investigate beyond the glossy brochures...two really terrible teachers have just gone from the boys school to big name indies...!