Michael,
I would agree that about 99% of the population do not care about a golf architects legacy, but like anything based on taste it is the 1% we are focusing on with this question (I think).
99% of the population do not care about wine or art, that does not mean it is not worth studying or discussing.
So for those who DO care about legacy, such as many of those on this site, does differentiation matter?
I agree with Andy's comment about land dictating interest in a course to a certain degree - but when you are discussing top golf course architects, they can turn a flat piece of land into something spectacular. Whether you think the Castle Course is a strong architectural design or not is certainly up for debate, but I think it is tough to argue that Kidd did not have the vision to transform a cow pasture, with a waste management plant in the middle, into something pretty amazing.
And this works both ways, look at what Kidd, Doak and C&C have done at Bandon. The setting for all three courses is spectacular, especially PD & BD. Someone could have come in and f'd it up. No? Would most people realize this, probably not, but that 1% would wonder about what could have been. Any of the above architects could have tarnished their legacy with a bad design, but they all challenged themselves and delivered.
I think Doak is a great study here because of exactly what Michael said - He took the time to visit, study, take in, meditate on, hundreds of courses throughout the world. He, probably more than most architects (I am not saying all), actually went to the school of golf course architecture and took the time to study.
This is what happens in medicine, law, business, etc. The greats in a field study deeply in that field - through study, they can take what they learn and turn it into something new and unique. In the case of GCA, they can turn it into something different depending on the land, setting, client's needs, soil, etc. They have 1000 ideas to work from instead of 50, it is a huge advantage.
If an architect has that depth of knowledge, it should show in his work. If an architect keeps returning to a "signature" or continues to apply a "formula", or mails in his plans and visits a course twice during construction, then I would argue that his work will get stale. His portfolio will get redundant and potentially boring, to the 1% that actually care.