Loading a .jpg into Photoshop and doing Save As sets the compression to what that image was previously saved with (thus you can see the level before saving it). However, resaving as a jpg always makes an image blurrier, regardless of the compression level used, since jpg is a lossy method. So, if you have one originally saved at level 3, it'll look slightly worse even if you resave as level 10 (and significantly worse if you resave as level 3).