I had originally planned on taking LA560 EZE-CCS, but the lack of D seats meant that I worked around it.

What I ended up doing was catching a bus from Buenos Aires Retiro station----acutally very close to AEP to Mendoza. In Mendoza I changed to a second bus for the trip to Santiago, as I couldn't find a direct service EZE-SCL. First bus was a AndesMar bus, can't remember which level of service they called it, but similar seats to a business class (non-flat) plane seat (but no IFE). Second bus was a CATA bus, and much more like what I'd consider a "normal" bus seat.

I was able to work it so that the longer trip (to Mendoza) was over night. 3-4 hrs in Mendoza and then the trip to Santiago was during the day. Some excellent views of the Andes if they interest you.

Approx cost $US100, duration including transit in Mendoza 28hrs or so.
Positives: Cheap, Los Liberadores Pass, Maximise South America D Sectors.
Negatives: Can't buy the international ticket outside of Argentina & LONG time with no IFE.

I understand most people would be more willing to just take a separate flight EZE-SCL, but thought I would mention this alternative.

From SCL I did end up flying LA560 in D as one of my sectors.

Oh and I don't plan on visiting Caracas again, as the city itself it pretty awful nowadays, and there isn't a great deal to do for more than a day. However I do plan on flying into CCS again, just going to the beaches/islands or Amazon instead of Caracas.