No. Because the icons are packed into a CSS sprite grid, you will only see the icons around it if you try to make the icon itself bigger (as you saw). You could increase the "size" of the icon by adjusting margin - but this won't make the graphic bigger - just the space it takes up.
Edit - Looks like the jQuery UI team has heard this complaint before and is going to roll out some larger icons in the next release of jQuery UI.
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