EA Sports' formula for sports games has been one of continual refinement year after year. Although the magnitude of the refinement may vary, it's hard to argue with the constant improvement. That being said, some years have more substantial improvements over others and this year, it's more on the light side. Question is, are the improvements enough for you?
The improvements made to NASCAR 07 are subtle, but not insignificant. The biggest two addition are the Dynamic Driver Attributes and the Variable Driver Attribute System. For me personally, both features add and sense of realism and continuity that brings more what makes NASCAR popular to the gameplay. Different drivers for instance have strengths and weaknesses that are more prominent, skill points are collected for good driving techniques which increase your own attributes from race to race while bad driving takes them away, and rivalries are created with an AI that can get quite a vendetta.
Other smaller improvements such as the graphics can be seen as well, although having a less obvious impact. Honestly it's hard to see a huge difference but there have been some improvements to the lighting effects and slightly more detail shown during the race.
So where does that leave us? Simply put, with a solid, well refined NASCAR game with all the modes from last year and new tweaks and modifications to the gameplay. Most fans will more then get their money out of it especially if you missed last year's version, but otherwise you might need to decide if the enhancements are enough to purchase again.