NASCAR has unveiled its 2015 rules package, and a summary can be found here, while a more detailed analysis is provided here.
Some quick takes -
The introduction of tapered spacers to the Winston Cup cars has been overdue with their success in the Busch Series and also the Trucks. Horsepower has been too high for too long, and even here 700-plus is still much.
NASCAR is also lowering gear ratios to keep RPMs at 9,000 and below - again, overdue, as escalating RPMs haven't done anything for the racing.
NASCAR has in effect put in a test ban for teams outside of Goodyear tire tests - given the failure of testing restrictions dating to 1990 and after, it's foolish of NASCAR to keep policing this.
Optional driver adjustable track bar - it will be interesting to see what to make of this on racedays.
"Knockout" qualifying comes to the Daytona 500 to set the Twin 150s - it's seemed to have worked overall, so there seems no reason not to have it for the 500.
Spoiler reduced to six inches form seven and change - six inches is not an unreasonable spoiler height. The goal of reducing downforce comes from the mid-August test at Michigan International Speedway; curiously, tested there were dive planes, small ailerons fitted to the nose near the hood, though they appear not to have made the final cut.