I've got the SPT exhaust on my car, and the headers are unequal length, giving a lovely warble sound still. With the new 2015, they did away with that sound in the name of 3hp and a drop back down to 2.0 liters of displacement.
While I wouldn't say that the cooling effect is totally mitigated vs. DI, I can tell you a very well known tuner melted many pistons before realizing that one always runs hotter in a mass produced performance car that is regularly modified. Yes... very vague
It is nice, everyone I have spoken with mentions the 2009 WRX's run extraordinarily rich; and definitely don't need to. I'm going to be running obdII diagnostics in the near future and get a really good feeling of how it performs before, and after.