When I first got got card college I skipped the material that I believed I already knew. With the exception of the top change and other techniques in 1 and 2 that I considered at my level, I basically jumped right into Vol. 3.
Even if (I would say especially if) you've been executing the material in the first few volumes for years; there is a wealth of information that will make your handling of that material cleaner, more deceptive, and which will enhance all of your card technique.
Giobbi is a rare combination a rich academic/theoretical/literary knowledge of magic, immense practical experience performing for real people, and a strong gut-sense for great magic. The finesse he brings (or calls your attention to) with items as basic as removing the cards from the box, holding the deck, getting and keeping a break...they're the kind of details that -- taken together -- are the difference between subconscious 'I-don't-know-what-happened-but-something-feels-wrong' and the sense that "he did nothing, and the magic just happened" (cf. the anecdote about Ramsay in the epigraph to Carneycopia).
I've found working through volume I to be very worthwhile, and recommend it regardless of your current knowledge base.