I have 2 panels that turned cloudy and difficult to read. They are resistive touch type. I believe capacitive touch type are not susceptible to this problem but are much more expensive.
Also, units installed outdoors usually require a brighter display. Because screens are sometimes moved around, we purchase all of our touchscreens as 'Hi Bright' units and turn down the brightness on the units installed indoors.
Brad Waybright
The more you know, the more you know you don't know.