I know that my 2002 LS-430 does the same thing. I'm not sure, but I don't think the trunk is designed to pop all the way open, but I have wondered about the condition of my struts too, since the trunk lid seems awfully heavy to lift open.
you can go to www.partsavenue.us it is cheaper than the price you mentioned. I also found a discount code that that site offers: 190602
I just had to order a set. Does anyone have installation instructions?