You can’t adjust the intensity of the Spot Remover filter.
What you could do though is use these filters instead, in that order:
Set the width and height of the Mask: Simple Shape filter to maximum (100%).
The mosaic filter can be substituted by one of the blur filters.
The intensity of the mosaic or the blur can be adjusted.
The Crop: Rectangle filter is used (with keyframes) to set the size and position of the area to be hidden.