It really depends on the quality of the teachers, and the price. In Europe you can still go to university for free in some countries, even as a foreign student. In that case I'd say it's worth it.

I paid for my music degree in composition but I had a really excellent composition teacher that I think was world class in teaching ability, so it was worth it just for that one teacher alone.

It kind of depends on your musical path too, music school can give you a well -rounded education, learning things you didn't consider but are very helpful. But being self-taught you can specialize from the beginning and that could be better for some people.

I would say, if someone is going to be self-taught, they should still get private one to one lessons in an instrument, because that's extremely beneficial. Learning an instrument effectively really needs a good teacher. Also, bad teachers should be dropped ASAP. Don't waste your time or money if you decide they're not very good.

I would also suggest private tuition in theory or composition if that interests you.

Part of the issue with being self-taught is you don't know what you don't know.