I like the simple plugin that you have created. I just have one improvement that you can make to make the plugin translatable.
If you replace this...
'View Your Shopping Cart';
_e('View your shopping cart', 'woothemes');
Also I found it complicated that you have three names for you plugin.
Woocommerce Nav Shopping Cart, woocommerce-menu-bar-cart and Menu Bar Shopping Cart. Please could you just chose one. As I could not find the plugin at first in the plugin area of my site.