[southernstar]

Unless you are interested in spinning your tires, the issue of unladen/unsprung weight has less to do with acceleration than handling and ride. Increased weight that is 'unsprung' - i.e., the wheels, tires and brakes (unless they are inboard), leads to increased upwards and downwards momentum of the wheels over irregularities in the road. So yes, the spacers will increase unsprung/unladen weight, at least partially defeating the purpose of light-weight wheels. They will also change your suspension geometry, increasing torque on the suspension components (remember the lever principle - the 'lever', with the suspension pivot points as the fulcrum, will now be longer). The difference may not be dramatic (depending upon the size of the spacers), but why sacrifice performance for appearance?

Brad