Good luck with the demo's.
Yes, I'm a firm advocate of bass shakers if your sub doesn't already vibrate your seat.
In my lounge, I have a little Paradigm PDR10 which sits on the floor (I have suspended joists and floorboards) right next to my sofa. Any large explosions transmit vibrations into the sofa via the floorboards and give the experience another diemnsion - a tactile experience.
In my loft, I didn't want to have vibrations going through the floor so I've tried my best to isloate my subs. They're also right by the screen so the vibrations would have further to go. The only way to get some tactile expereince was to bolt some bass shakers to the seats and power those via a seperate amp which gets the same LFE feed that my subs do, so the seats only vibrate with 80hz and below.
I think CPC do some shakers now, and they occasionaly come up on ebay, so try there if you think you may need some extra tactility.
Gary.