You would need a program that resizes mesh files....they do exist but I've never personally used one nor do I know how well they work...

AxelDude used one for his Infinite Stars mod to make all the meshes (and some effects) smaller....I know he had some problems with it though, and he was making the meshes smaller....

Since you will be making them bigger, I'd imagine you are going to lose texture quality (since the textures will be stretched more)...how bad it will look I do not know....