I've taken the opportunity to rewrite the directory stuff, using wxStandardPathsBase where possible and putting everything into a class that is kept as static instance in ConfigManager. That way, file paths are determined once per application, not once for every namespace (as it is now), and all the checks whether special paths exists are also only done once, instead of once for every namespace.
The only problem so far is that wxStandardPathsBase::GetUserDateDir() crashes on my machine... it seems to hit a null pointer inside AppendAppName(), humm....