Looks like a Qlikview question.
May I ask how the user would know it was something to maximize and not just a piece of text?
Most people that use a product prefer consistent indicators of functionality. Personally I wouldn't focus to hard on things that are astetic and will only cause confusion to the uses if implemented.
also looks like a QlikView question to me.
Perhaps this solution is suitable for you.
It is possible to have any textfield as a button to switch different diagrams on another layer to become visible (move to the foreground and in the background again). So there is no need to use minimize option in the usual way.
In the tutorial video, there is an example how to hide/unhide filters: