I don't know if PIAA HID Super Plasma Bulbs are any good, but if you are looking to improve visibility, without blinding oncomming traffic, simply changing the bulbs won't work. BMW HID is a multipart system which includes reflector geometry (to properly aim and focus the light), xenon gas bulbs (greater brightness), and self leveling system (to prevent the focused, bright light from blinding oncomming traffic).
Do whatever you wan to your high beams since those aren't used when other cars are around, but do the rest of us a favour and don't hack your low beams and blind us.