Ok, a quick glance at the specs (and the title of this segment!) answers some of my questions and may answer yours as well. Regarding 40 mpg and whether that is a significant move ahead or not–
Following the trend of auto makers the past 10 to 12 years yes and no. Despite adding content- gps- traction control- a/c as standard- the highway mileage has actually increased. Following the trend of the past 3 years- decreasing engine size, increasing gear numbers, improving aerodynamics, all appear to come together to allow GM to advertise 40 mpg. The downside- is this slight increase over the present Aveo despite bring out a completely new car with a different engine and drive train and more aero appearance is not a real move forward in terms of getting a direct replacement for the current car. The reason for the content"improvement" is pretty easy to decipher.
The move from amortized costs on a platform that has been largely the same for 9 years and built by a workforce that draws presumably a lower cost per unit wage means that the shift to a US built replacement almost required both a name change and a marketing shift upward that allows GM to make money. To justify that expense it's fairly standard to offer more "features" or "content" to sell the greater cost of buying.
For someone interested in buying the spiritual and low cost per mile replacement for the Aveo, the Sonic isn't it. The new Spark probably is.
Steve