The Stasi documented what they did in quite some detail and most of the documents were not destroyed during the fall of the wall. So, there is no need for speculation.
I'm by no means an expert on the matter but as far as I know, the Stasi did not disappear political opponents regularly, at least not after Stalin's time. I looked over the article and didn't find that claim but if I missed it and it's in there, then the article is wrong about it. The Stasi had a large array of measures at disposal. Some people were cleared for moving out of the country to West Germany. Others went to prison. Some people were exposed to radioactive materials. Others got a better job that moved them away from other dissidents.
Specific "Zersetzungsmaßnahmen" you and the article mention were very rare - we're talking about an estimated few hundred to thousands cases in total. When they occurred, however, they were extremely devastating because not even experienced critics of the system imagined them. We're not just talking about switching socks and replacing good milk with spoiled one in the fridge. There were also cases of medical doctors prescribing the wrong drugs, for example, worsening the symptoms of diseases.
As far as I know, who became the victim of these special measures may not have been a fully rational decision. It seemed to be based to a large extent on the preferences of the case officers in charge.
Broader measures against critics of the system were far more common, however, and way more pervasive than what most people suspected at the time. For example, the father of a former girlfriend of mine was a famous GDR rock musician. He later found out from the archives that the Stasi planned and supervised his whole life and managed to break up his former band without anyone suspecting it. One guy moved somewhere else for work, another went to prison, and he moved elsewhere, too. There were also way more informants than he ever suspected. Basically, the Stasi and their informants interfered with what other artists he met, were he and his band mates got work, and so on. They planned over years. It went far beyond the usual method of giving people a telephone and letting them hear a loud click when the tape was switched on (they did that, too!).
> it seems very unlikely to me that using resources to troll someone like this provides an effort/reward ratio that would be interesting to someone with that much existing power
Nevertheless, this happened. The Stasi was a huge bureaucratic organization with ideology at its core, built after the example of the KGB. Stasi officers considered themselves fully in the right, defending their people against counter-revolutionary and decadent activities. Goals ranged from "helping" citizens get on the right track towards socialism in a friendly but firm manner, over collecting information about potential adverse political activities, to completely destroying enemies of the state and doing counter-espionage.