I have iDrive & the Apps package in my car. TO answer your questions, you do not need the cradle to work with the Apps package. There are some interesting features, for example, you can have the iDrive system read your emails to you, you can post to and read from Twitter and Facebook and RSS while driving, which seems like a bad idea. You can also stream radio from all over the world, which is kind of cool.
Thing is, a friend of mine who has a 135i with iDrive just had the system take a dump. It was covered under warranty, and the dealer's solution was to order a while new unit from Germany. This is not to say it was the only solution to fixing the problem, but it got me thinking...
1 - I am hoping to keep my car for a while, if something was to go wrong with the iDrive system, I can't imagine the fix would be cheap.
2 - Unlike an Android phone, or iPhone, the OS in the car, while you may get a few maintenance updates via USB, I think it is very unlikely that BMW will offer an upgrade from version 3 to version 4 (I don't know what version they are actually on, just using numbers for an example)
3 - The map upgrades are prices similarly to buying an after market GPS. I have a Garmin in my other car, and it has traffic, lifetime map updates and was a fraction of the price of the iDrive system.
Considering the above, personally, while I really like the iDrive system, and being able to copy music to the hard drive I really like, I kind of wish for reliability sake, I had forgone the system.
Just my .02
I don't think you will be disappointed if you were to find a 1M!
Good luck on your search...