Using a vector representation may be a more practical approach as retina-style screens become more pervasive. Microsoft Research has an interesting paper on this from last year's SIGGRAPH: http://research.microsoft.com/en-us/um/people/kopf/pixelart/
That said, once you switch over to more advanced scaling, the artist loses a lot of the fine control over the result that can really make pixel art shine.
The technique in that paper kills the effect completely. Its a way to de-pixel the pixel art. Also, vector representations quickly become much more CPU intensive. Would be more efficient to scale the pixels as suggested above.
That said, once you switch over to more advanced scaling, the artist loses a lot of the fine control over the result that can really make pixel art shine.