How brake pad dust/residue affect braking and rim life?
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.