Currently, using the scroll wheel while the mouse cursor is in the minimap doesn't do anything. I would expect the view box to scroll with the wheel at a speed proportional to the decreased size of the code.
So, for example, if a single scroll wheel motion moves the normal window 3 lines, and the minimap is a 1:12 reduction, a single scrollwheel motion over the minimap should move the main window 36 lines.
I edit many files that are > 1000 lines and this behaviour would be a significant help! I'm still a ST newb though, so maybe there is already a preference to enable this?
Edit: Oops, please move to the Ideas and Feature Requests forum!