For me, the question of whether to bring Microspikes or not would be based on a guess at how extensive the snowfields are, as well as what times of day I'd be likely encountering them. Hiking through the Sierras in June on the PCT, I found that traction devices were rarely something that I wanted, and in some of those times when I might have, there were intermittent bare spots where you might be inclined to take them off (though microspikes in particular are pretty good for doing short bare ground patches). This was true for the particular year that I hiked; I make no claim about other years!
Hiking through much of Montana in June another year I did find the Microspikes well worth having. Much more extensive snow, and the microspikes held up (and otherwise worked) great over quite a lot of use.
On the AT in March on a high snow year, yaktraks worked very well, insofar as the biggest issue there was stretches of ice, not the snow. There was a lot of snow in the smokies, but for whatever reason I rarely had traction problems that I recall other than on significant stretches of ice.
Hiking and snowshoeing just around home I find that it's a little hard to predict whether I'll want any sort of traction or not. If I'm hiking up an extensive forest service road to access the area I'm going into, however, I'll typically bring microspikes.
So IMO it's pretty situational. Reasonable tread on trail runners is just fine for a significant subset of snow scenarios in my experience, and in the experience of a lot of other long distance hikers I know. The trick is properly estimating what things will be like for the particular trip you're contemplating.