I wash/wipe the blades almost every time I wash the car to remove the accumulated road film. That gunk will effect performance
whether the blades are a week or a year old. I just use the soap & water straight from the bucket...I've used wipes like the 303s
and found no difference just using soap & water. But Dack's right, get your blades replaced for free at the dealership annually
(especially if you drive your 1er year 'round).