Get Workbook Method(s)
I will not mention again that I find the outdenting of Dim statements hurt readability. Instead I'll focus on this part:


On Error Resume Next
    Set wbTest = Workbooks(strTargetName)
    IsWorkbookOpen = (wbTest.Name = strTargetName)
On Error GoTo 0



What error are you expecting to trap here?


Workbooks(strTargetName)



This will raise runtime error 9 - Subscript out of range. By then you already know everything you need to know.


(wbTest.Name = strTargetName)



This will raise runtime error 91 - Object variable or With block variable not set - but you already know if that call is going to work before you even try it.

This would be cleaner - slightly overkill with error-handling, but cleaner:

Public Function IsWorkbookOpen(ByVal wbFullFileName As String) As Boolean

    On Error GoTo CleanFail
    IsWorkbookOpen = Not Workbooks(wbFullFileName) Is Nothing

CleanExit:
    Exit Function
CleanFail:
    Err.Clear
    Resume CleanExit
End Function


Notice the difference between strTargetName and wbFullFileName: "str" says "that's a string". "wb" says "that's something about a workbook". Both are Hungarian, only one of them is doing it right. Avoid prefixes that indicate the type.