It is worth it if you have the money, however, the difference between the swissvax kit and picking and choosing your own products is that #1 it's cheaper because swissvax stuff is expensive
, and #2 some products work better than specific counterparts in the swissvax arsenal.
I haven't used too many different products to compare so I'll let the other detailing gurus chime in. The most popular product, though, for two of the categories you listed are: Sonax Full Effect Wheel Cleaner and Stoner's Invisible Glass. Edit: Oh, and for leather, the two most popular ones are leather master or leatherique.