"wipe the dust from you sweet smile" - I always thought it meant that they hadn't smiled in a while: things get dusty when they're not used. I think that Lucie is racing ahead and her partner/friend is trailing in her wake, and she's trying to persuade him to stick with her and enjoy the journey, and chase after their dreams rather than letting life pass them by.
"wipe the dust from you sweet smile" - I always thought it meant that they hadn't smiled in a while: things get dusty when they're not used. I think that Lucie is racing ahead and her partner/friend is trailing in her wake, and she's trying to persuade him to stick with her and enjoy the journey, and chase after their dreams rather than letting life pass them by.