I think you need the 8500 model to get the "appradio" functions for android. If you really look into it, you'll see that on the lower end models, a lot of those cool features only apply to Iphone. I have the 2500, which is the same as the 5500 I believe as far as apps/compatibility, and I can't do anything thru the USB. I can connect via BT for phone stuff, audio over BT and pandora.
Even thru appradio, you are just using built in apps on the headunit, using the phone for gps and/or data connection. If you root your android, there appears to be something cool called ARLiberator, where you can basically turn your HU into a remote screen for your phone:
I looked into it when researching headunits, but ultimately said screw it and just got a basic double din unit. Me personally, I rarely use/need navi on the go on a daily basis, and I have a good garmin with lifetime map updates to use for big trips, etc. I feel the phone/car integration piece is coming along, but not quite 'there' yet to be extremely useful.