I've not done any suspension service on the WK yet, so I'm not totally familiar with it...however.
The upper arm should include new bushings as well which is never a bad idea. The lower should include one of the bushings if bought as an assembly, if I recall correctly.
If your bushings are in good shape, I would just do the ball joints and save that coin. But by the time you factor in bushing cost you're possibly further ahead to do it all together now and save the labor of replacing bushings separately.
08 5.7 Limited WK - Basic stuff...