It is going to screw up the handling.
'Looks' are cool, but unless you plan on riding the bike in a straight line as long as you have it.....it ain't worth it!
IF you just want something 'cool' to ride around town, (Lot of people where I live do what you're talking about...super fat rear tires, etc.) you'll be able to impress people that are easily impressed.
People that can actually ride bikes on roads other than 'flat and straight' will think 'squid'.
It's your call, it's your bike. I mistakenly assume most people would rather improve handling and performance, than degrade it.
I forget people ride bikes for different reasons.....
Does anybody remember those magnifying panels they used to sell for TVS, to 'turn your 19 inch set into a BIG SCREEN TV!'????
Maybe we can make up and sell a mudflap/rear fender thing made of the same magnifying stuff? The rear tire would look 'big', but you wouldn't screw up the handling!