Mast rake

I'll say at the outset that i do not race, so the answer to the following may simply be that on the water performance is the sole determining factor, but here is the question. I assume that for a one-design class, the maximum allowed area of the jib is defined so why is the recommended rake of the mast dependent on whether a loose, snug or tight rig jib is used? I have North recreational main with a Schurr furling jib (which is probably a bit smaller in area than a hanked-on jib) and I adjusted the rake so that I had just bit of weather helm close hauled and verified that I also had weather helm when sailing full-and-by and then further off the wind. Do the different rig tensions affect the effective area of the jibs significantly (??) or is it just that without a backstay, the Scot mast rake cannot be changed on the water and the mast rake is selected to be the best compromise for all wind strengths. Do I make any sense at all?

Yes, Monroe - you are on the right track. 
Within the one-design jib parameters, sail manufacturers have determined that different jib cuts (shapes including chamber, chord, etc) are better suited for a particular mast rake and forestay tension.  Generally, forestay tension defines the loose, snug, or tight rig. 
In his book, "Sailboat Racing with Greg Fisher",  Greg discusses mast rake and rigging in depth.   From his experience, Greg strongly advises sailors to set the rig to the sail makers specifications to eliminate variables.  The rigging guidelines by the sail manufacturers are based on water performance. Please note, that part of their performance criteria is to minimize weather helm.
Hope this answers your questions.