That's an Aloe - Aloe saponaria, is my guess- not an Agave.

And I did not know that the maculate A. saponaria is also known as A. maculata. Well, everyone knows a plant worth its cambrium has at least two names, if not more.

Aloe saponaria, aka soap aloe or African aloe, has a rosette that is up to 1-1/2' tall and about the same width with lance-shaped leaves that are thick and succulent, armed on the margin by sharp, dark-brown teeth, and pale green with white blotches or spots. The name comes from the Latin sapo for soap, and saponaceus means soapy. Sap from the succulent leaves makes a sudsy foam in water and thus can be used as a soap substitute. Its synonymous name maculata refers to the white spots on the leaves. Soap aloe is native to arid regions of South Africa, Botswana and Zimbabwe, and is a very drought-tolerant species. During the summer it sends up a branched stalk about 2' tall, bearing showy tubular yellow, orange or red flowers. It propagates by producing little "pup" rosettes around the main one

If you ever get a chance to see it in the suburbs of San Diego (which, you will grant me, is closer than Cape Town) you will know the truth of the last sentence in your description above - it's enthusiastically puppiferous.