This is my first newly purchased vehicle as well. Before this I owned two 1996 Jeep Cherokees. The first given to me by a parent, the other purchased cheap when the first had a tree fall on it. Most of my car knowledge comes from that side of things, always a wilderness lover at heart. I needed an economical vehicle for getting around though, so the Sonic was a good choice.
I've no experience with turbos before, though I understand the basic principal behind them. I read the post you refer to talking about all the various issues that can be had with turbos. Above my head for the most part, but I could follow along.
Before I bought this car, I rented a Buick Encore for a week. It's basically the Buick version of the Sonic, though maybe closer compared to the Trax that is coming out for 2015 here. It had the 1.8L engine. It felt sluggish. It could get around, but had no 'spirit.'
I knew from using that Encore though that the interior of the Sonic would fit my needs well. Very spacious for a small car. Being that I work for GM, I would be able to get the best purchase on a GM line vehicle, so that ruled out the subcompacts from other brands.
The first time I drove the Sonic with the 1.4T, I knew I loved it. The stock engine was far more spirited than the Encore's 1.8. That said, after the tune, it's about the same difference from the stock 1.4T, as the 1.4T is from the 1.8. Which makes sense as the dyno reports for what the tune can do, show about that much increase in torque.
I have also seen about 2mpg increase in my combined hwy/city average from before the tune when spending most of my time in eco mode. Not much but it's enough to make a difference in the long run.
