The value of a Thermarest is a very personal thing but for me it's well worth the money. I think the Yoke is PLCE item so that squaddies can do the daypack thing with their bergen side puches. I suspect that the reason they don't have the daysack fittings on the ordinary yoke is that they would be painful under a heavy rucksack.

As for weight, you can can get much lighter rucksacks with a similar volume, eg check out Golite UK , look at the Gust pack, about the same volume but weighs only 590 g yep grammes! It's about the same price too.

Justin