Need advice on GPS for Scenic Drives in Z4 Convertible

Hey recently took a scenic trip across the twilight zone in my Z4 convertible. The twilight zone known as rural Mississippi where they don't apparently believe in route signs, speed limit signs, now entering or any other kind of signage. Really had fun when my cellphone based GPS system lost all contact with the known world. Had visions of Mississippi Burning.

Anyway decided I need a real GPS. Would love to hear from anyone that has experience with a good GPS for a convertible and scenic drives in the $250.00 dollar or less range. Here is what I am thinking I should look for in terms of features.

Must Haves
_____________________________________________________________
Portable
Very bright screen..can hardly read my phone one in the sun.
Excellent speaker for dealing with wind noise.
Very sensitive GPS receiver
Very good alternate routing algorithms
Spoken road names

Nice to have
_____________________________________________________________
Downloadable maps from external sources like mad maps or google.
Free Map updates
Waterproof
GPS tracking
Altitude as well as latitude and longitude
Points of Interest

Not sure I care but might be nice
_____________________________________________________________
Traffic Updates...doesn't tend to be a lot of traffic on scenic routes anyway
Voice Command
Blue tooth Phone Integration