in general, STV would cut down on tactical voting a great deal, simply because it makes it harder

Possible counterexample:

In the USA, tactical voting for President is usually completely impossible, due to the electoral college system. Your vote only affects the election outcome if the election as a whole is a toss-up and if your home state is in play. But for a Texan like me, that will never occur, not even relative to the one-in-a-million odds you'd normally expect from a national election. If the Democratic candidate stands any chance of winning here, they'll be winning the rest of the country in a landslide. Likewise for a Californian: any situation in which the Republican might win California is a situation where they've surely already won nearly everywhere else. Likewise for most of the country; only a handful of states, known well in advance, are "swing states" in a given election.

Yet, other than a few weirdos like me, does anyone use this freedom-means-nothing-left-to-lose situation to vote for a third party and thereby at least influence news results? Granted that most people usually prefer the two leading parties' candidates, but I haven't seen any statistics which would suggest that the minority of voters who disagree are likely to vote their consciences except in the swing states.

It may be that, even if many Democratic/Republican voters would legitimately prefer other alternatives, they appear to vote tactically due to some other bias: the human desire to "vote for a winner" tempered by the desire to avoid voting for a completely unpalatable candidate, or the desire for group affiliation expressed in this case via political party identification, perhaps.

What baffles me is that even the news media here does first-past-the-post polling! Asking people to give ranked preferences to generate official election results might be a serious legal undertaking, but why in the world doesn't a single major news company or polling organization ask for ordered preferences either, even for primary elections when there are often a half dozen serious contenders in play?