How can I change the default currency key on Swype keyboard?
Looks like a problem with the version of Swype pre-installed by Samsung. I have logged a bug on Swype's forums here. Don't think there's anything much any of us can do now except wait for Swype to fix the bug and for Samsung to push out the updated version.

(just adding this as an answer and accepting to get this off the unanswered questions list, if anyone has a better solution please post and I'll transfer the acceptance over)