In my experience, most people over think and over do their wash. If you put soap on a car with a dispenser, a foam gun, garden sprayer or whatever, let that sit on the top surfaces while you do the wheels and below the belt line, then just rinse the top with a good hard spray of water, the only thing that should be left on the top is maybe some bug spots. Then, just use a nice plush and slightly damp microfiber towel to dry from the top down, one quick pass to get the majority of the water off, then blow out the cracks and door jams etc. with a master blaster, the rinse out the microfiber tower and wring it out and go over the car again and there shouldn't be any marring to speak of. Oh yeah, the bug dropping should have come off in the first pass with the drying towel.
If the car is truly corrected and sealed before you use this method you'll be fine. If on the other hand you just fill and glazed your car, the scratches you filled and glazed will re-emerge - it looks like you marred your car, but really, you just never had it right in the first place.
Robert