I think the problem with the Graal store merchandise is that it's too amateur looking. The images are far too complex for a Graal t-shirt. You need something simple like this:
It's really crappy gfx and badly put together but the general idea is there....
Instead of just slapping some gigantic ugly character or a screenshot or something on the shirt... just make it a little logo with simple colors and some text. (I don't have Graal's font so deal with it) I just think it's the whole idea of having a shirt with a cartoon character on it that turns most people off.
This is coming from a guy who has a domokun shirt and a shirt of shigeru miyamoto's face. You can still use characters they just can't look like cartoons.
edit: The only way you'll get me to wear a shirt with a cartoon character is if the artwork is simply amazing. I have a Trigun shirt but the art is so badass that it's okay that it's a cartoon drawing. It looks like a piece of art and not just some colored doodle.