Sorry to hear about the burglary. That is a rotten thing to happen to someone.

I think you may be confusing image quality with depth-of-field or something else. Because image quality isn't affected at all by focal length. In fact, the Canon 70-200L lenses will blow away your 28-135 in terms of image quality. I know - I have both. However, depth-of-field does decrease at longer focal lengths. For instance, at f/5.6 at 200mm you will have shallower depth-of-field than you would at 135mm and f/5.6. But image quality has nothing to do with focal length. Image sharpness, contrast, color, saturation, etc. are mostly a result of the quality of glass used. That means how well the lens elements are ground, matched, the coatings used, and the actual quality of the materials used. And the Canon 70-200L lenses are among the best ever. You will notice the difference and probably wouldn't be happy with the 28-135mm after using the L lens.