I got me a copy of the big fat book by Smart et al. today! But it dates from 2006. Are there any major areas of datedness to warn me about?
wxWidgets just released 3.0 – the most recent “stable” release. The book to which you refer most likely relates to 2.x; Audacity requires wxWidgets 2.8 and will not compile with 3.0 (without major changes to the Audacity CodeBase). The book should be just what you need if you are intending to work with Audacity and wxWidgets in combination.
There have been major changes in wxWidgets between 2.8 and 3.0; while there are a lot of new features and there is a lot of backwards compatibility there are significant problems with incompatibility.