Some of this depends on what you mean when you say "VBScript." VBScript is an entirely different thing from the script hosts that use it.WSH is somewhat deprecated because the .Net types want to promote their PowerShell doodad. However Vista and Windows 7 contain newer versions of WSH, MSHTA, and the VBScript engine itself. Getting at the "new features" in the newer VBScript can be tricky, I think the only way to "turn them on" exposed for general use is in IE 7 and later (and perhaps MSHTA - the host that runs .HTA applications).
But books in general have dried up for economic reasons, except for the most mainstream of technologies. VBScript is still fairly mainstream, but there isn't a large amount that is new about it. Book sales tend to follow what is new or trendy, because more people buy those books. There just isn't much reason for a publisher to produce new books on VBScript.
.Net languages go through a spasm of techno-churn every 2 years or so. This makes them better fodder for new books on an ongoing basis.