No, you don't have to do it, any more than you have to use any poly bushings, but they really work well with IPD's stiffer antisway bars -- after paying money to buy the complete kit, why undermine what it's supposed to achieve? That's my only reason.

Like I wrote, the new links come with new rubber bushings already installed -- they're fresh, and hard! I didn't have a press handy to push them out, so I had to drill holes through them in a circle to make them soft enough to push out with a vise. It's a bit of work, not a LOT but it is the most time consuming step in the whole installation (in the front, that is), but not impossible. And installing the poly bushings in their place is really easy -- they slide right in, especially with some spray of soap (e.g., I used Simple Green).

I recommend going for it -- when you order your antisway bar kit, also order the lower bushings.