D-reame
I have just fitted a becker cascade which is basically the same unit plus sat nav build in. I bought an 18 month old unit off eBay at about 50% of the price you would pay on the web.
I also bought the iPOD interface for £70 (cheapest I could find on the net).
To say I am chuffed with the Becker is an understatement. The sound quality has improved tenfold over the stock unit that was in before. (I am still running standard speakers).
Bluetooth is excellent, synchs with my Nokia 6500 without a hitch and call quality is as good as on my top of the range Merc unit. The only down side is that you have to manually bluetooth over contact details to the unit one by one. It does not automatically download all of your phone book as my Merc does.
The iPod interface is the best I have ever used. Full playlist, album, etc... control from the head unit. It is just like having your iPod in your hand. You can easily run the interface cable into the glove box through the latch hole without any drilling at all (I had to remove the latch to get the head of the interface cable through and then reattach). I leave an old (version 2 I think) ipod in the glove box which will not charge as battery is knackered and it works like a dream.
I have not fitted a head unit for over 10 years but I fully wired in the Cascade incl GPS antenna/phone speaker/iPod interface in 30 minutes. It was a doddle.
I can't comment on the Alpine unit but I really do think the Becker unit is worth the money. Personally I don't like my dash to look like Blackpool illuminations (but I am getting old
). The Becker really does look the buisiness, blends in perfectly and does not shout "nick me".
Why don't you look on eBay, you could get the indeanapolis unit (same but has sat nav) for the same money or less (one went for £170 last week). Make sure the unit is under 2 years old and you get the original sales receipt /delivery note and Becker will honor the 2 year warranty (I have this in writing from Becker). Try and get the red display as this matches the Z3 dash the best. Also check software is v3.6 or higher else may not work with iPod interface. Mine is v3.61. The latest version is v4. Therefore my map is probably 2 years old but for the saving I can live with that. (Its £170 to get the latest software and maps so bare that in mind). Obviously make sure you get all cables (microphone, GPS antenna) and security code with it (its on a credit card). The manuals can be downloaded from the Becker site.
How do you rate the speaker? Where they easy to fit? Would you get the same ones in hindsight? I may look at upgrading in the summer
I think I turned the setting off on the Becker thinking there was no GAL signal. I have had to adjust volume manually temporarily when on the motorway. I guess I should check if the wire is there for pin 10 and turn the setting on it it is 
This should give me auto volume increases and I know where I am in a tunnel 
)
