I don't know how changing the display of instruments on your screen could be, on average, any easier than it is now. Having a + or - on a dedicated button would only be quicker if you only had two different instrument layouts. With the current method, you have a maximum of two clicks whether you have two layouts, or 5.
One thing I did discover is that if you have a certain collection of instruments on you main screen, then enlarge the EFIS, those instruments that were there won't necessarily be there with the half or full screen EFIS. You need to make a separate instrument layout for each different size of the EFIS, as well as for different orientations of the screen.