I'd say SGP comes the closest that I've seen, in some aspects, but is still quite different overall. Shambala remains quite unique compared to any of the other ~15 festivals I've got recentish first hand experience of.
I've not yet been to any of those named on this thread, but have a friend who speaks very highly of Beat Herder (there's a very high chance I'll give it a go on his recommendation next year) - although he makes it sound more like a Festival for people who used to like Boomtown, but have grown up (maybe even had a kid) and can't be arsed dealing with the hassle or that crowd anymore.
The same would be true of Shambala, in my opinion. The above said, it's like the Dyson advert which states 'If you want something that works like a Dyson, it has to be a Dyson'.
