Layout Plot Configurations can vary from a named page setup, so there isn't a Layout.PlotConfiguration property. You just have to get the individual plot settings. Something like the following.
Code:
Private Type PgSetup
CMN As String
CenterPlot As Boolean
'Add more props here
End Type
Public Function GetPageSetups() As Collection
Dim PgSetups As New Collection
For Each lyt As AcadLayout in ThisDrawing.Layouts
If lyt.ModelType = paperspace then
'get desired layout props
Dim PgS As New PgSetup
With PgS
.CMN = lyt.CanonicalMediaName
.CenterPlot = lyt.CenterPlot
End With
PgSetups.Add(PgS)
End If
Next lyt
End Function