Strut bars make the biggest difference when your really throwing the car into the turns. Its purpose is to tie the sub frame and the shock towers together to create a solid "box" from top to bottom. You might not notice much just cruising around corners but if you take them quick, the car will have crisper turn in and with less body roll. IMO they are worth it but dont spend any more than $150 on one, any more is a waste.
Sway bars:
Addco.net They make a rear LS400 sway bar that I currently have on my LS and it REALLY kills the body roll. Front sway bars are hard to find for the LS but I believe forum member Hypronet had a stock set sent out to be re made oversized and from what he said this company carrries front and rear bars now, ready to order. I dont have the company name but Hypronet does. Hope this helps!