Wanted to circle back to this thread and thank you all for the support, suggestions, feedback. It has been a LONG application season: first app submitted in October and deposit just now submitted in late April. Tshirt ordered for “senior day” next week!
This month we took some crazy trips to see colleges, in some cases flying in at 9AM and out at 9PM. Some were DIY and some were official. In each place we found a spot where kids seemed to be coming and going and congregating, and we just sat for a while watching and eavesdropping. 
At every school we visited he seemed happy. And he carried the various swag water bottles and book bags etc with real ownership and optimism. It was exciting to see him feel the “fit” and/or the potential of each place. But there was one school where I could tell “this is the one” within 5 minutes of walking onto campus. He had stopped talking and was just taking it all in. I think he was almost nervous that he’d found his school, that the long search might actually be over. The tour guide introduced herself with pronouns and we did as well (I think son almost swooned saying he/him). He was electrified the entire day. This was his people. This was his place. I’m absolutely thrilled to report that he will be attending Macalester!
What did it was the contained campus, the students (down to earth, unpretentious, happy, friendly, outgoing), and the fantastic urban area. He truly felt right at home. And I cannot imagine him going anywhere else. He is so sure about his choice that he has declined all waitlists (even for more “selective” schools). He is resolute in his decision. And I am grateful for all the advice on this thread!