Torque Boxes? Do I need them
I have sub-frame connectors and it was amazing how much it stiffened the car up. Before I installed them I could jack the car up at the torsion bar cross member or the front spring mount and wouldn't be able to open the door or if it was open the latch would be off by 1/2". Now with them I jack at either point and both wheels come off the ground at all most the same time and the door opens and closes easily. The other very noticeable thing is the squeaks, rattles and grown of a 40 year old car were dramatically reduced.
As for Torque boxes the factory installed them in convertibles and big block cars and didn't install frame connectors so there must be a significant amount of stiffening. It's on my list to install both front and rear torque boxes but just haven't gotten around to it.
Anything that stiffens the chassis will allow the suspension to work better and will reduce rattles and squeaks so I would say it's worth it.