Ok found more details about the mystic Pioneer blue/white wire:
* The reason I'm so unsure about this is because the installation manual said "never connect blue/white[sic] wire to the power terminal of the audio antenna. " That sentence messed with me big time.
Insalling a Pioneer HU and have a Blue wire and Blue/White wire extra.? - Yahoo! Answers
" Connect the blue wire in your adapter harness to the blue/white wire in the Pioneer plug. Your vehicle has an in-glass antenna, and it uses an antenna amplifier to improve reception. The blue wire in your adapter harness is the activation wire for the antenna amplifier.
Since your Pioneer deck probably does not have a blue (power antenna) wire, you need to use the blue/white amp turn-on wire to activate the Nissan antenna amplifier. "
" That blue wire coming out of the back of your receiver is a remote wire so that when you run an amplifier your receiver will send a signal through that blue wire and tell the amp to turn on and stay on. The radio AM antenna is that big, long metal plug that goes into the (more than likely) right, back side of the receiver. Make sure that that plug is all the way in. I listen to the radio just fine and all I have plugged in is my antenna (big metal plug), Front speaker wire, red ignition wire, yellow power wire and black ground wire. "
So it seems like the BLUE/WHITE wire from the pioneer deck is used to send power out to the remote amp, and I can also tap that wire so the power goes to the BLUE wire in the harness and hence powers up the glass antenna in the xB.
Gosh I hate finding extra info every time I put the deck back together.