I would like to have seen High Pointe, and Belmont, in Richmond, VA.
I had intentions to see Belmont, but procrastinated until 2 weeks before it shut down for renovation by DL3 group.
As others have mentioned, I would love to have seen the greats as they were originally. Namely Ojai, Augusta, and others from the Golden Era.
Not necessarily for the architecture, but I would have loved to see some historic matches in person, like "The Match" with Venturi, Ward, Hogan, and Nelson, the 1913 US Open playoff, and an early Open with Old Tom.