What is the significance of the final section?

While you have two fine answers already, it is important to note that Persky warns Kugelmass against using the machine again.  The underlying note is be happy with what you have...in the present.  However, Kugelmass insists, and while the machine is working, Persky has a heart attack, the machine bursts into flames, and instead of the novel Kugelmass expects to end up in, he finds himself in the middle of a Remedial Spanish textbook. Not only is the "large, hairy" irregular verb tener (to have) chasing Kugelmass, it is "over a barren, rocky terrain" that this occurs.  This description of setting again supports the idea that it's not getting what you want in life that is happiness, it's wanting what you have.