I have found the info in Lenz' book to be basically bulletproof species-wise. It is a go-to book if I've got questions on some species.
Collecting techniques can also be translated across regional lines and species--what works for a vigorous tree like a wild apple in New England will probably work for a vigorous elm in Va.
Superthrive is a particular quirk that some people insist on hanging on to--it was just coming into "style" among bonsai folk around the time the original book was written and published.
Further review and experience with the Superthrive the "magic elixir" however, has tempered opinions of it. Personally, I find it useless and potentially harmful if used in large quantity. The crap is driven by Barnum & Baily-level hype--just read the obnoxious label. The "tests" it cites were performed by the manufacturer for crying out loud. There is no list of ingredients and the user has to rely on faith that its worth the $$.
If you're buying the book for info purposes, get the later edition. If you're into collecting books, get the first. I have both, but I bought mine when they were first published years ago. The first edition of the book was printed, if I remember correctly, with help from the American Bonsai Society.
I had hoped when it came out that it might spur other more regionally-focused collection books... Didn't happen unfortunately.
