I've come across this a couple of times. Usually people create a LocationRect from a collection of locations used by pushpins and then set the view to find that some of the pushpins are out of view. This is because the LocationRect does not take into consideration the pixel size of the pushpins and only focuses on the coordinate. In V7 we have an option to add a padding but this same option isn't in the Windows Store SDK. I wrote a blog post a while back on how to calculate the best map view based on a collection of locations with a buffer (). Using this I put together this reusable method for calculating the zoom level for a bounding box with a buffer. You can then use this zoom level and the center property of the LocationRect to set the map view.
public double CalculateZoomLevel(LocationRect boundingBox, double buffer, Map map)
{
double zoom1=0, zoom2=0;
//best zoom level based on map width
zoom1 = Math.Log(360.0 / 256.0 * (map.ActualWidth - 2*buffer) / boundingBox.Width) / Math.Log(2);
//best zoom level based on map height
zoom2 = Math.Log(180.0 / 256.0 * (map.ActualHeight - 2*buffer) / boundingBox.Height) / Math.Log(2);
//use the most zoomed out of the two zoom levels
var zoomLevel = (zoom1 < zoom2) ? zoom1 : zoom2;
return zoomLevel;
}