Interesting...I thought it was just us who had a slightly blurry rear window. We have a VX-II Lumina, 2002.
I have never understood why it matters what tint you have on the rear window. In fact, as far as I knew, it was OK to have whatever you liked. think logically about it...if you have a ute, and have a load of crap in it or a canopy, you can hardly see out the back anyway. If you have a van, you simply won;t see squat out the back. Come to that, putting a set of rear window louvres on will restrict visibility pretty effectively.
I would just go for it on the rear window...we will probably get something like 25% on the rear, and leave the sides as they are because, as yet, they haven't done anything funny...touch wood...:whistling