>>18
Beautifully explained.

>combining the subjunctive form of "もらう"

My preference is not to use words used in English (or related languages) grammar for Japanese grammar. In this case, English sentences using the subjunctive form are often expressed in Japanese using 仮定形, which もらおう is not. So, it's confusing.
There is the more language-independent and linguistically oriented word.
http://en.wikipedia.org/wiki/Desiderative
I've seen it used for the type of ending in question here, which is classified as the second 未然形 in Japanese school grammar. But this word might sound too technical.