Hi Ben,
I'm new to Lexus but have been a Toyota owner for many years. Just purchase an 04 GX so I understand your plight. Some of my online research has turned up a lot of users going for items from this company: http://www.oemautointegration.com/99-11/lexus
They seem to have most of the bases covered for Sat, USB, BT, iPhone, Android etc integration.
I've also considered looking through the auto recycle yards for a next gen nav unit but at the moment I'm looking into more basic things like whether to buy the service manuals on paper or on CD and where the best place to buy parts online.
Good luck and keep posting!
Ken