What does Didion primarily admire about the underground press?

In "Alicia and the Underground Press," Didion praises the underground press for being unabashed about the opinions of its writers, thus exposing authorial bias but allowing the reader to form their own opinion with that information in mind. For Didion, writing that pretends not to have any bias at all inherently clouds or skews the truth, whereas writing that is open about its leanings or purpose is more truthful.

Why does the trip to Hearst Castle, San Simeon make Didion feel regretful in "Trip to Xanadu"?

Didion becomes saddened, at the end of "Trip to Xanadu," by the realization that her own image of Heart Castle in San Simeon was more lyrical and powerful when it remained just that -- a mental image -- and that it had lost some of its magic the moment she laid eyes...