I just lowered mine with the eibach pro-kit a couple weeks ago, and there's no reason you should need to replace them unless they're broken or something.
I would get the poly sway bar bushings and the poly end links. The poly end links can be bought at Murrays, but the sawy bar bushings you want to get from Mustang Parts & Accessories - 50resto You need to measure the bars thickness before ordering. Mine were all cracked, and I went with polys. Much better handling.