Update May 5 2019
My Plugin has been suspended / removed from the the WordPress Dot Org repo because of Trademark Infringement.
I am working on removing the trademark infringement but until I do – please checkout the Github version. Which I promise I will maintain far better from now on https://github.com/digamber89/woocommerce-preview-emails

Update: 02/02/2016
Hi guys(& gals),

One of my first tasks as a WordPress developer was to make design changes to WooCommerce email templates and check that template. There is no default way for users to do this. To resolve that issue i’ve created this Plugin Woo Preview Emails

I’ve been working on an extension for WooCommerce to preview email templates without having to manually send them.
It’s on Github.
It is now both on Github and I also have a plugin for this on the WordPress Repo https://wordpress.org/plugins/woo-preview-emails/

Basically What it does is add a Preview Emails section in the admin area via which you can choose the different email templates. All the kinks haven’t been worked out yet but you can see the generate templates and hopefully it aids you in editing templates quickly.

Most of the kinks have been worked out, it works perfectly well for all the default email templates. I’m currently working on a way to do this for all and any 3rd party extensions that adds it’s own email templates. I haven’t had enough of requests yet for that feature so, if and when i get some input back on it i’ll start on that as well.