Well, 1) I would fix the EVAP code issue first.  Knock sensor will show
up piggyback with many other emissions codes.

   Once I was sure the knock code is of its own source, replace it.  The
ECU is the final judge as to the performance of a sensor or part.

   My symptoms were decreased highway mileage - currently my mileage for
mixed driving has increased by about 4mpg slowly over the last couple
thousand miles.  The engine has more pep - as a 5 speed owner I notice a
blip of the throttle with clutch in has no hesitation like it used to.  It's
also more apt to bite hard if I give a lot of throttle on an exit ramp.  The
fuel mileage thing may improve further - I suspect I've got bad control arm
bushings that cause the car to wander and grind away my front tires.  The
front tire wear is nauseatingly evident after only 6k.

   Dave