I haven't actually used the speakerphone much on my 6600, so I can't tell you how loud it is.

PowerNavigator doesn't do route planning or turn-by-turn instructions at all. It's a fairly simplistic program. You can download maps as bitmap files, but you have to create them yourself (export them from a map-making program or something). Once you have the maps on the device, you can manually set waypoints etc, then PowerNavigator will show you distance & direction to the next waypoint.

If you're looking for a proper in-car navigation system, then I'm not sure if there's one available for Series 60 phones.