Difusers on the speakers?

Folks have been surrounding their tweeters with thick felt for ages. This can lower off axis information and help quiet a bright sounding driver. No so much on other drivers. Good DYI project for a rainy day. Cheap and easily reversible if you find it is not beneficial.

OP, FWIW I can't imagine what/why diffusors in front of the speakers would do anything dissimilar to putting a blanket over them (assuming I'm correctly visualizing what your thinking about). 

Interesting thing about having wide baffles, it can improve bass/low midrange response and give a more pleasing sonic balance, at least more so than having  curved surfaces on a tall narrow speaker. (All typical caveats apply.)

If you want to play around with controlling sound with devices placed near or on your speakers which in essence creates a 'live end/dead end room. It won't necessarily have any WAF but it can get you a sound that has less room affect than others. Place sound absorbent panels immediately adjacent to both sides of your speakers (extending out in front a foot or so). This helps kill any sidewall reflection points and back wall reflections (if your speakers are toed in). I did this many years ago with some commercially available 6 inch thick dense foam rubber 'U' shaped panels. Just amazing how it cleared/cleaned up the sound. I learned a lot in the process but then I didn't have a dedicated room, i.e. one without a wife. So it goes/went. :-)