Will try to help answer your questions, but you will have to pick through the info since I'm not sure exactly what you mean by "make a difference".
Cal-trac's & other similar devices when installed properly are "just along for the ride" anytime there is not sharp forces being applied from the rotation of the axle...simply as the axle rotates (pinion upward) as the tires start to rotate forward. The lever on the bottom bracket turns this motion into pushing. The push on the front pivot plate turns that motion into holding down on the spring where it will buckle up as power is applied.
So do they work on the street? The question then is? What are you trying to "fix"? If you have 400+ RWP, steep gears, hard as a rock tires, a light backend & slippery roads...are they going to make you not spin? I highly doubt it. If when you "put some boots to it" on the back road & you get wheel hop & shake from the spring wrapping up, then yes they should work fine. There is NO magic...simply levers & fulcrum
As to the question about the 2 leaves. I use 3 & if I put much weight in the bed without air in the helper bags, in goes to the snubbers REAL easy. I think 3 would be minimum. Lorne