Isso parece funcionar:
Function OnlyNums(strWord As String) As String
Dim s As String
s = Replace(strWord, ",", " ")
s = Replace(s, ".", "")
s = Replace(s, "'", " ")
s = Application.WorksheetFunction.Trim(s)
ary = Split(s, " ")
OnlyNums = ""
For Each a In ary
If IsNumeric(a) Then OnlyNums = OnlyNums & " " & a
Next a
End Function
A única parte complicada era descartar o ponto decimal e limpar alguns outros caracteres especiais.