Other than built-in wifi and size, how much difference is there between the older GoPro Hero 2 and the latest Hero 3+ model? It would seem not much, surprisingly. At first glance anyway. 

To sort out GoPro post workflows for the coming Solar Challenge I did an unscientific test over the weekend: I set both GoPros to 1080p at 25fps, bumped up both cameras to Protune recording mode, and then recorded the footage you see above from different positions. Other than increased clarity on the Hero 3+ there's actually not too much difference between the two.

If I need to take only one camera I would prefer the Hero 3+ because of it's size, weight and wifi (and, yes, clarity), but in situations where you need to mix footage from older and newer GoPros it seems there won't be too many post headaches if you keep ProTune enabled.