@eur0_2! Your spark plug indicates your bike is in perfect condition. For more information, check the following picture:
Carbon on Exhaust Tip:
If its wet then its your piston rings. In this case, bike will give a blue-ish white smoke when warmed up (nothing when cold). Thats because the piston is sucking up the engine oil and burning it while the piston is firing. (check some images on google to see the position of rings on the piston, to get a better idea how piston rings block that engine oil to get sucked up in combustion chamber).
To check if the carbon deposit is Wet or Dry:
- Dry carbon can be "dusted off" with a simple blow from your mouth. Its like powder.
- Wet carbon despots tend to "shine" when put under sunlight or halogen light (or your bike's headlight).
As you said your bike has only done 11k, and assuming you have driven the bike carefully, i don't think your Piston Rings are at fault here.
Instead, get the Fuel Mixture checked ... because a high fuel mixture (which are genuine setting on new bikes, and most mechanics don't change it) can leave unburnt fuel in your exhuast, which muffles its sound, and may reduce the "crispiness". (But thats also because of changes "tappet adjustment" ... and there is nothing you can do about that. Buying new exhuasts will be a waste of money)
Mud Flaps below the engine increase the wind resistance, hence the slightly reduced mileage. It can also decrease the top speed.
Its better NOT to use a "Metal" one which covers the "whole" area below the engine. Use the plastic ones and dig some holes in it, so that wind can pass through.