Like it or not, it sure is unique and really sets your Mustang apart. With your current wheels on, its got a "Street Machine" tucked wheel look and thats a strong trend among the high dollar custom builds right now, i think you would clean house at the car shows.
If it were my car, i would go 20" and fill those fenders with a really wide rear wheel, as much as you can fit. Reminds me of the ground effects kit from the Fox Body Saleen.
I like when people take chances and do something different, Congrats on a job well done! Alot of widebody kits look like ghetto after thouhgts, your fab work looks awesome.