That sounds like a very frustrating issue. I'm sorry I don't have a good answer for you, but one thing that may help temporarily is pressing the HOME button on the keyboard. This should reset the scene and reset the DPI on the mouse wheel in the particular scene. Also, if you hold down the Mac equivalent of CTRL, then press down the middle mouse scroll wheel to engage the precision zoom. The issues with the wheel could be caused by any number of settings in the user preferences, such as Navigation > Orbit & Pan > Auto Depth. Turning this on could resolve some issues with mouse wheel navigation. Also, in the properties panel (N), enabling Lock To 3D Cursor could help with viewport navigation in some circumstances.

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