It is definitely worth the OS upgrade for many reasons, but not the specific questions you ask.

The OS upgrade will not change the behavior of the altitude-- it is only visible when the unit is not navigating.

You may get some better turn information if you upgrade the OS, but I am not sure. (I have been on the new version for so long that I can not remember what the older OS views look like.) The Garmin units will give you a mock view of a road with lane lines, and stuff. The newer BMW MKIII OS version has a split screen view that shows the map and the turn instructions in the same screen. It is not as detailed as the Garmin, but it does a pretty good job.

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2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input