I think you should have it but I don't need it.  here is the thing when the tires are pointed forward caster will have little to no effect on tracking. (it will effect spring rate and some other stuff but that is not the point I am getting at)  you could have one wheel with 5º positive caster and one wheel with 5º negative caster (talking front suspension now) it should not effect handling (assuming the suspension stays static and the track is level and smooth), however the second you turn the tires, even a little it will have a drastic effect on handling, so in your case where you are wanting to have some built in steer than a little caster is probably a good thing, but on my car where the tires are always pointed the same way  it should not have any noticeable effect.

I fully agree, I just used the different caster to illustrate that it would make little difference when the wheels are pointed forward. I also got to thinking if caster returns the steering to center could it not also help return your rear suspension to normal ride height when coming out of a corner. 

Think about it (I brought this up before but was never able to effectively get my point across) You are wanting your rear wheels to "steer" as a result of suspension changes.  At normal ride height the rear wheels are pointed forward, but as the suspension changes some "steering " is created.   Then if you look at it in reverse and  add a little caster then as you come out of a corner and begin to straighten out the wheels should want to return to straight which should help return your car to normal ride height.  make sense or am I not explaining it very well???