Andrew,
Most creative personalities will tell you that constraints can inspire creativity more than a blank canvas.
Since my first day on gca.com, I have tried to dispel the myth of the "perfect routing" for any piece of property. Most archies develop 2-30 prelim routings quickly, analyze them, throw some out, combine the best features or others, etc. And yes, the owner typically is involved to at least review the pluses and minuses of both.
I recall sitting with the late Robert Dedman when he said that returning nines add about 3,000 rounds to any course. I may have even asked him in response to a similar thread years ago. He had similar opinions (based on operating hundreds of courses) about sun positioning. What architect will say no to one of the most successful owners ever? And ask them to willingly give up $$$ to accommodate your vision of a perfect golf course? Short version, there just happen to be things that are more important to a golf course than some random design feature that the gca and about 10% of golfers would recognize. And of course, if that hole is never built to some compromise, who would know it was missing to tell us that another routing would be better?
Beyond that, all design is a compromise of sorts. I would guess, based on my experiences, that on most sites, you can work returning nines and good sun angles for opening/closing holes without compromising much in the design. The hardest ones are when the site offers the most convenient clubhouse location somewhere on the western part of the property, when it can sometimes be impossible. So my answer to the sun question is, "great to have, all other things being equal."