Re: Apple aren't one for banishing people only to pick them up later at a discount
Some of your points are characteristic of Apple, but others, while logical, aren't necessarily used.
"I'd guess that most countries have at least some legal impediments around driving the value of a potential acquisition into the ground; if nothing else, there's a definite overlap with the kind of predatory behaviour which anti-monopoly laws are meant to address."
It is not clear. Using a monopoly decision to do that is illegal. But there are many other methods which are not illegal. There is a certain amount of activity which gets dismissed as "bargaining well for a better price" and therefore accepted. In this particular case, the app team have a reasonably good case because Apple abused its monopoly position, but that would work as well if Apple didn't want to acquire them. I.E. it's only Apple's App Store monopoly which makes that happen rather than another law.
"The first is that if the acquisition has value to you, then it presumably has value to other people/companies. So if you do drive the price down, the odds are good that someone else will step in and buy it at a higher price."
Good point, although it doesn't apply much for this example. The app in question works on phones and watches, but there are lots of keyboards for phones. The IP in question is for their watch app, as their phone app is still permitted on the App Store. There are only three smartwatch platforms with enough functionality to make use of a keyboard with the multitouch and processing requirement of this keyboard. Apple is by far the largest. Samsung's platform is believed to be dying. So the only other purchaser is Google, whose platform is also not in great health. Given that Apple has the most users and that the app doesn't run on Android at this stage, they're by far the most likely to buy it.
"Another point is that by driving the value down, there's a risk that you'll lose the things which made the acquisition valuable. E.g. the target may sell off some of their assets to stay solvent, or lay off people with the domain knowledge needed to make the acquisition valuable."
Again, not a bad point but it doesn't apply in this case. The tech is a single application, although some of its functionality is open source released by another developer. The staff is two people. Not all that much they can do except try or give up.
"And if it becomes known that you're responsible for driving down the value, then people may choose to leave the target of their own accord rather than working for you."
I doubt that's a factor for most acquisitions. Apple can hire new developers to understand and develop a codebase. What they need most is the code that already works and the rights to any patents involved. It's a bigger problem when there are lots of people and the acquirer wants to keep that running, but for something IP-based like this, not as much.
Your final point about PR problems is good and applies.