What a great thread/topic!
I got cut off on my last post as we had to run to the park to play on this wonderful day.
I think the answer to "how important" it is can only be answered by the individual. If a person only has ever played one golf course and they love it beyond all imagination, then breadth of experience isn't important. They've found what they love and they are happy.
If the individual in question is seeking to learn about golf course architecture, its history, it changes, adjustments, growth, etc. I think "breadth of experience" is vitally important.
When I first started managing money I was inundated with Modern Portfolio Theory, which essentially implies markets are efficient, investing is purely a risk/reward decision. I personally thought that MPT was a bunch of garbage that academics with little real world experience dreamt up. But having only a Bachelors degree and little experience managing money, no one really gave a crap what I thought. So, I went on a quest to gain respect and have the "checks in the box" necessary to have my beliefs/opinions carry some weight. 12 years later, I've have earned the right to use the Chartered Financial Analyst designation, I've got a track record managing money that beats the S&P 500 over almost anytime frame, I developed personal valuation models that seem to stand the test of time and changing markets, I've got market models that also seem very robust, and I've got the test scores and experience to get into many quality Finance/Economics/PhD programs. So, now when I say MPT theory has its flaws...more people than not, listen.
I think the same might go with golf courses and golf course architecture. On this site, it happens all the time when disagreements occur that people inevitably say, "have you played course X?". If not, opinions are dismissed. If yes, the next question is "how many times?" If less than the person asking the question, then opinions of the other are seemingly diminished. And all that is fine and dandy, if people want to have active debates and have ammunition for winning them. However, I will say that from my life experience simply have 20 years of experience (or playing 1000 golf courses) doesn't necessarily mean all that much. My friend articulates this theory well when he says, does Joe Schmoe have 20 years of experience or does he have 1 year of experience 20 times over...essentially saying does he learn through his experiences or not.
Nevertheless, for me the real important piece of the puzzle is having the knowledge and experience to fit all the moving pieces together and have a real understanding of how things began, progressed, went right, went wrong, and what is next around the corner. To me this is fun and interesting. But to the next guy it might not be. So, as I mentioned early...the level of importance regarding breadth of experience is solely based on the weight each and every individual gives it.