I would probably pay a little extra to guarantee an empty middle seat.
But, I wouldn't pay 3x to be able to lie across a row of economy. With about 60 inches to work with (Astana 752 seat width is 18.1in), I think I would be uncomfortable trying to fit in that space. If I recall the last time I had the ability to lie across an entire row, the seats are not very deep, so I always felt like I was about to roll off.