The {{unbound}}
helper doesn't work as a block helper and can't be used with {{each}}
You always need to use it on a specific property like this:
{{unbound myProperty}}
See this thread on github that discusses this issue: https://github.com/emberjs/ember.js/pull/1457
The good news is that until HTMLBars comes out (last I saw was they are shooting for Ember 1.8) you can use the {{group}}
helper. It's not part of ember core but I have used it succesfully with Ember 1.5 and it will get rid of the metamorphs for you (as well as data binding).
Download it here:
The easiest thing to do is just copy the contents of https://github.com/emberjs/group-helper/blob/master/packages/group-helper/lib/main.js into your own helper.
Then you can do:
{{#group}}
{{#each items}}
<span>{{unbound myValue}}</span>
{{view App.MyView content=this.subItems}}
{{/each}}
{{/group}}
Note: As stated by Robert in the comments below the {{#group}}
helper will also affect the view itself.
Hope that helps!