Yeah, I believe you really only need powered USB if you have lots of stuff that draws its power from the USB port (i.e. keyboards, mice, flash card readers, USB wireless adapters, etc.). Things like scanners, printers, and external optical/hard drives use their own power supplies, so they don't need one.
If you plan on getting more peripherals that require powered USB, just get a powered USB hub. No need for a USB PC card just to add a couple of USB ports. It's just cheaper.
morkman