You technically don't "need" to replace them completely, however, an aftermarket set of RLCAs sure do make for a nice mod.
You might want to check the upper control arm bushings while you're there just to note whether or not they're shot. If so, best to just replace them completely with FRPP ones ($70 maybe) when you get the time and patience.
I replaced my uppers and lowers at the same time and I can't even begin to tell you how many squeaks, creaks, and so forth went away, not to mention the significant improvement in rear traction and handling.