I was wondering if you could make a View Level button, for using the Observer like in the LE, where you can fly, but with this version you can't place your marble and you press esc to toggle it. I was also wondering if you could have a zoom control (the scroll wheel) and get closer or farther away from your marble.
Your first idea could be done by just modifying/disabling some of the camera code. While it is theoretically possible to have a second camera similar to the Observer (ask HiGuy, he's played with this a bit), this is impractical in the end due to the fact that it's deprecated, weird code. I would recommend just using the Observer camera but changing the controls.
As far as zoom control, are you now referring to the normal camera? Check the DefaultMarble.cameraDistance, cameraMinDist, and cameraMaxDist fields. I don't recall if MBG's input has mouse wheel support.