There's no sense in upscaling past the minimum required size: it won't add quality to the image. A 500x500 pic won't be improved by being scaled up to 3200x3200, it'll just add more opportunities for artifacting.

To artists: please draw at high resolutions already. Seriously. You won't lose anything from your pic being 2000 by 2000 or higher unless you're running a literal potato, because you can just zoom out and enlarge your brushes a bit.