If you tow or load a fair amount of weight in the rear, I would suggest it. If it's just a daily driver with the normal kid load here and there, I would not feel it would be necessary. Still can't go wrong with it. It's not like the older system I could have had on my 99' E/B Expedition. That system was an air bag system that had issues. On the 07' it's a self contained shock. I have a similar design on my Mercedes, and it has proven to be wonderful.
I have a 2000 without and a 2007 Limited WITH the RR load leveling. We tow a 7000 lb.+ boat that probably has 400-500 tongue weight. On the 07, the rear height stay perfectly level, on the 2000 the rear end sags several inches and makes the front end and stereing feel "light" due to less weight on the front wheels. If you are EVER going to tow more than a few thousand pounds, you'll want it.