FWIW, the Vista DOES have WAAS - I use it all the time. I have had my Vista for a couple of years now and it has never let me down. I have dropped it, dunked it, and used it both professionally and for GeoCaching and it is always rock solid & bulletproof.
The screen has never been a problem for me (I typically nav with the compass screen & custom settings (maps are nice, but unless totp, generally just eye candy unless you are urban navigating or using the GPSr as a trip computer & navigation aid.
You want to play MP3? Get a iPod
Why? Well, when your batteries run out because you have been jammin on the hike in you are not gonna be happy that you can't find that cache
My .02 - YMMV