How brake pad dust/residue affect braking and rim life? You know the dust that's left on the rims' groove after a while, does it have any significance in braking or rim life? When washing the wheels I just realised that the dust must be coming from brake pads but couldn't figure out whether or not I should wash the wheels more often to keep it clean. Will I make the pads and rims wear out faster if I clean more often?
Cleaning the wheels regularly will probably help the life if the brakes, but most likely only modestly. The most important reason to clean the wheels is to remove the road dirt/grime that builds up and can wear on the pads faster, but the brake dust most likely isn't causing undue wear. 

Cleaning the rims shouldn't adversely affect the life of the rim if you are doing it correctly and making sure that the rims are dry after cleaning.