well.. 2 independent ID's ... if its scale.. its treatable.. but i have never seen such on mature bark ... if its mushrooms.. as bboy suggests.. i think.. lol ... they are living on the rotting wood under the bark ... time is limited ... that is a very bad prior pruning.. i am wondering what the prior owner did to the rest of the tree ... two more pix .. as good a closeup as you can get... and a pic of the whole ... may as well tell us where you are also .... ken ps: why am i wondering if this tree was topped.. or telephone poled ... or any significant construction in the root zone... or all three????

I don't know about the Agave, but the cactus looks like a Trichocereus pachanoi that's seem some hard times. It will take a light frost, and maybe a little freeze, but it is from the (relatively warm) hillside of the Andes. A good measure to use is no wet feet when it's cold. You should water it in its growth season (now).

this looks like scale to me too. I had this happen to my jade plant. I treated it with http://www.bonide.com/products/garden-naturals/view/025/bon-neem-ii. I spot treated mine with that solution diluted with water and used q-tips. A problem I ran into was if I didn't catch it early enough they were embedded and hard clean off. I used the product above for a while, but when I missed a few days of treatment it had spread to the other leaves, I had to cut off all the leaves of the plant and hope that it would grow back. It did and it's doing fine now. I hope your plant can recover!

Definitely a Clivia