I have used the hi-res on/off option as a method to enable/disable display zooming because it is consistent with the users desire not to use images that are blurry. It is the same concept for vector maps as the maps are rendered to produce a raster image before the zooming is applied. Of course teh zoom could be applied before rendering, which would make the make always the same quality, but I wanted to make very few changes outside the plugin.
THere is another option that I prefer: that is to incorporate display zoom into the core and then the hi-res option could be changed to enable/disable display zooming. In the various classes that adjust for high density displays by introducing a scale factor (currently 1.5), this can be removed and let the user select the amount of display zoom desired.
With raster maps in particular, the text is often extremely small wnen displayed on hi-res screens - to the point it is almost impossible to read (especially if your eyesight is not perfect).