Yep, way too much hassle, and all for a system that can't hold a candle to all but the very cheapest personal navigation devices. There advantages to the factory system (mainly from an anti-theft point of view) but the disadvantages, hassle and cost swing things very much in favour of an after-fit sat-nav/stereo unit or a personal navigation device.
Some personal navigation devices will need an external aerial to see through the Laguna windscreen. If you get one that has the SirfStar III receiver chipset (e.g. TomTom Rider, One, 510, 710 and 910) then you won't have this problem.