Sorry Z! I must have been sleeping.
Well, I rode my dealers 'naked' 1250 yesterday and the difference between my faired bike and the bike without the lower fairing is minimal.
By comparison, my FJR was way better for protection but the Bandit isn't in the same league (or price bracket). I know that my legs feel a stronger breeze on them than they ever did on the FJR and that breeze is hardly different from the stock bike.
So, bottom line - the lower fairing to some will be cosmetic only. To me, it's largely to minimise road muck being thrown onto the engine thus causing corrosion (I've also got the fenda extenda and rad guard).
The fairing probably helps to a small degree but the biggest improvement for protection from the elements has to be what you've already done - a better screen and those hand guards.