For what it is worth- here is my take on spreader rake after having to re-rig mine. I am assuming it generalizes beyond my boat.
The more spreader rake the more you can induce pre-bend which, in the end, depowers the rig. This can be adjusted with the diamond wire tension (if there is spreader rake, if they are 90 deg then you wouldn't be bending anything really). I was told to not use a significant amount of prebend because I sail with a heavy crew (less pre-bend= more power for heavy crew). I assume high-end sailors will adjust their diamond wire tension to suit the conditions. The problem I have with all of this is this- I have about 1.5 inches of spreader rake with diamond wire tension actually pretty loose at about 250-300lbs which induces about 1.5-2 inches of pre-bend (maybe the mast is shot, who knows). Now add a spin and everyone starts talking about diamond wire tension more (to limit the S-bend). If I torque my diamond wires more to try to prevent that s-bend then I will end up with a lot more pre-bend than is necessary. Add to this is the fact that tightening the downhaul induces more pre-bend (thus depowering more) but doesn't really limit the s-bend (I think).
Well, I hope this gives you some idea about spreader rake,etc. I think I have succeeded in confusing myself