I was in the same boat - wanted the navi but didnt want to wait months.

It looks like the dash piece that is around the radio/navi is a seperate panel (shouldn't need a whole new dash).
There are some really cool aftermarket units that retract into the dash, but Id like to get one like Hondas.

I think the factory install came with a different steering wheel as well - it has a mic for voice activation.

"There is no spoon."
Neo "The Matrix"