Are the £500 helmets worth the extra?

[Dick Dastardly]

I'm looking for a new lid but the choice is huge. In one bike shop they spent ages telling me why a Shoei is worth three times the cost of a similar looking HJC (something to do with a hard outside layer and a soft inside layer, and visa versa), whereas another shop said they are barely different.

Any of you lot know the reason? Did you decide to go for a really expensive one? Thinking about a Shoei for peace of mind (and the brilliant inbuilt sun visor) as a main helmet and wouldn't mind a cheaper spare as two of them would cost as grand.