HI Guys,
Keeping the struts inflated definately saves a bit of time, but as others have pointed out the hot car thing is BAD. Also consider that the struts do very slowly leak air so every couple of days you will need to top the struts up anyways.
The main concern I have found is that the necks of the valves get stretched from having the caps inserted all the time and they become quite loose, you need to then be careful about the velcro covering.
There is a method of sorting out stretched valve necks. Place them in hot water for a few minutes, then cool them in cool water. This normally works well.
Leaving the struts inflated also relieves some of the stitching failure of struts commonly associated with folding the struts to fit it into the bag time and time again in the same spot.
Summary: There are as many pluses as there are minuses to leaving them inflated. I like the compactness of the kites when packed so I always pack mine down completely, but at the end of the day it is whatever works best for you.
Good winds,