It would be nice if they made them easily removable, but since the purpose is to keep the cover from getting messed up from a tank bag, I understand why they'd attach it with some pretty rigid glue. The stickers on my cover have moved slightly by themselves, so I can imagine something like that X would get moved all over the place if the glue was any softer.
As far as headlight polishing kits, I tried using one we had left over on the back of my black airbox. The previous owner put a sticker on the back in the place of a buckle guard, and when I pulled it off I found that it had started to eat at the plastic. It was flaking off almost like fish scales and was faded to a lighter color. I sanded it down(although probably should have started with a rougher grit than was provided in the kit), all the way down to polishing it. It looks worlds better, but it's not perfect, and it's still a bit dull. Eventually I'll probably but some more sandpaper and try to do it again, and eventually will cover it with a tank guard. I just don't really like any of the 3 options we have available for our bikes so I haven't wanted to put out $40-50 for something I thought was uglier than the messed up plastic.
I understand why people don't like the X, I prefer the look of the cover without it, especially the transparent ones, but I get very paranoid with things bungeed to my back seat because I can't see them. Aside from a tank bag, I could probably even just bungee things to my airbox cover if I had the X on it. Hopefully enough people will read the instructions here, pull theirs off, and there'll be a bunch floating around that I can grab one for a couple bucks. [up]