2001 S430 P0130 P0140 P0400
 

230 K miles, running fine, threw a CEL just before I took it to the dealer to possibly trade it (it must have overheard me discussing this).

The first 2 codes indicate O2 sensors on opposite sides. I'm assuming that these codes are symptoms of something upstream. I have no personal experience with EGR valves, but from the reading I've done, it seems like the first things I should check for are blockages in the metal tube going from the EGR to the Intake manifold, or breaks in the plastic tube coming from the EGR.

Does this sound right - namely that I should ignore the P0130 and P0150 codes for the time being and focus on the P0400?

O2 sensors are designed for approx 120K miles.

Yes cleaning or replacing the EGR tube is a good starting point for P0 400