-how do you account for these spiritual remnants-

How about "overactive imaginations?" Not necessarily a bad thing, because we need to remember what happened at these places. But the "ed" on that word (happened) means past tense. Some people are more "sensitive," which is another way of saying that they have a hard time dealing with the concept of past tense.

Sorry if I sound a little cynical, but I was out at a Civil War battlefield the other night with a group of ghost-hunters, complete with IR cameras, tape recorders and EMP detectors. Nobody wants to find ghosts out there more than I do, but they're not there, folks. Their spirits may well linger on there, but they don't jump out and say "Boo," and they don't play parlor games with electronic equipment.