It's kind of cute. Much better than
Marcia, although I usually hate nicknames as given names. I had a friend in high school who had a cousin named
Marcy, who was a child back then, but I never met the cousin as they lived a couple hundred miles away. Other than that, I've never known a
Marcy.
There is the Peanuts character, but that's not a bad association.
Marcy has never been on my radar, but I wouldn't say I hate it.