I think it would be great to create some addon such as Thunderbird has - it is called quicktext. It enables you to define some standard replies and then simply paste them in your replies. Something similar to “signatures” function, but it could be a little bit more sophisticated.
if our Templates function is not so satisfying for you, I can add your request to our official feature requests list and we will consider more sophisticated version of it.
I would be happy with signatures, but a hot key to get to them without clicking with a mouse would be nice. Such as in OE, alt+i, than s and you can select it with cursor keys.