On the advice of an actual graphic designer I also tweaked the logo a bit. The flat slabs of color in the original design look fine in smaller items like patches and pins, but come across as a bit bland when blown up into larger sizes. A touch of shading helps fix that, providing some dimensionality and visual interest.
I'm going to give the same treatment to the expedition logos over the next week. Here's a look at how the revised Antarctic logo will look with shading. It's relatively subtle, but provides that ever-elusive "pop".
One feature of Zazzle's apparel printing that I'm not crazy about is the premium on dark colored clothing. If you'd like a T-shirt, but don't want to pay an exorbitant amount, try fiddling with the color and styles selector on the ordering page. Switching the base shirt to grey can cut the cost nearly in half. You can also put the design on things like heavyweight hoodies, which is pretty nifty.