Not much power gain, to be honest. Maybe 5hp at the most. You will notice a gain in gas mileage. And you'll notice less lag, especially on colder days. It sounds amazing too, especially with the V6 engine.
I lowered my journey with H&R Sport springs. 1.5 in the front and 1.4 at the back. It lowered almost 2.5 inches after it settled. You'll need 2 new end links and a 4 wheel alignment. Other than that, no problems at all. Check out my gallery (titoboyjourney).
Your Journey looks so sick! I have a 2010 SXT FWD and I've done a few things to it too. I am currently looking for tail light covers to give it that tinted look. I would also like to find a way to change the inside of the headlights to a different colour.