I rode a Sora equipped bike for about 10,000 miles and my wife has one full Sora bike now which she's put about 1000 miles on and another bike with just a Sora rear derailler with about the same number of miles. None of these bikes have ever ghost shifted. Neither of the two bikes with Sora front deraillers had any more problems with chain rub than I've had using other much higher end deraillers (assuming it's in tune, it will stay there just like any other front derailler).
Sora triple shifters do in fact have a trim position when in the little ring. You can easily use the full range of the cassette in the little ring with this trim feature. My Sora bike (Specialized Sequoia) had long enough chain stays that I had no chain rub when using the full cassette range in the middle ring too.