I think it's tough to call Taconic overrated, as it's really great, and despite its length of only 6700 yards, the landing-area slopes and elevated greens make it play longer.
Also, I don't know if Cape Arundel is underrated. While I am a big fan of the course, its tiny, fun greens and funky chocolate-drop mounding, I think it gets quite a bit of attention due to the presidential connection. It's only known nationally due to its constant mention in the press. If the presidents summered somewhere else, the course would be a classically-styled hidden gem of 5900 yards with a sleepy feel (much like York Golf & Tennis in So. Maine). Without all the celeb/pro visits and secret service, it may be underrated....