I like leaving kits sealed, it not only makes it look nice, but, it also keeps everything in the box and I know it is a kit I have not started! And trust me, I start lots of stuff some times!
But, I have had to unwrap some kits due to the wrap shrinking and crushing of the box, or the wrapping is so brittle that is is falling apart every time I handle it.
Plus I like it when some old kits still have their original price tag!