STIs plus BarMitts...
...have revolutionized my morning winter commutes. I can wear a thinner glove and slip my hands into the Mitts and then have both comfort and control.
As to the OP's question of ease of changes, yes. When you're still deciding on how a bike will be set up, it is simpler to some degree. But this doesn't matter to me, as I don't begin building until the concept is finalized, so once and done.
I have downtube shifters, bar end shifters, flat bar combined shifters, and drop bar STIs. When I go from riding a non-STI bike back to the drop bar STIs, I'm reminded of the convenience of shifting while standing, or actually simultaneous front and back shifting, or the finer control that more rear cogs with smaller steps give.
This morning I rode a 2 x 6 friction bar end shifter bike in to work. The gear jumps are more coarse on that bike, and I was thinking how finer tuned one of my STI bikes would have been. Not a big problem, but the either the power needed or the cadence suffers...