Yeah, you can't wait for other people to go with you, you definitely have to go alone. You certainly need to head to Slab City, sorry you will miss getting to meet Leonard Knight, creator of Salvation Mountain. Sounds like you will have plenty of activities to keep you busy.
That will be a good base for visiting San Diego and checking out Yuma. We loved Yuma when we stayed there. It is a darling little town.
Is your land anywhere near Laughlin? December through February seem to be great months for tootling around in those areas. Plus, you can hang out in Quartzsite that last week of January. That will make me very jealous! Tee hee
Is there any way that you can bring your cats with you? If your friend offered to feed them for free, then it was her responsibility to keep them fed. No matter what, they were in her care so I think you have a right to complain.