I don't think Spotify through an Android phone would work in the Blue and Me system...
The Blue and Me uses the dock protocol when communicating with an iOS device, which Spotify on iOS can hijack and present itself as though the iPhone was playing anything from its own library.
However an Android phone would present itself as a mass storage device (like a memory stick), which Spotify on Android has no way to communicate with so it would likely just ignore it and play through your phone speaker instead.
I can vouch for the Gateway BT Lite, have one in my 159, it hijacks the CD Changer port on the back of the head unit, allows A2DP and calls with steering wheel controls. It's a good system, the only downside is that you don't get track names, instead it displays CD05 Track 01 etc.
Edit: you could store your music as MP3 on the Android phone though and plug that into the USB port, that should work. As long as the phone isn't running a too newer version of Android where they changed the mass storage protocol too I think? (Could be wrong there though)
Hope this helps, cheers, mike.