I was really thinking of the predicament that Immaculate Conception finds itself in, not a soul living within a mile of the place (I think there is one new downtown loft a couple of blocks away, but other than that and Georgia State University, nothing.) It could find a niche as an historical church, but it's a little anomalous -- they've moved the altar out from the gorgeous old reredos, and it's a very "contemporary" parish - which doesn't exactly lend itself to historic preservation. I only attend on weekdays, but if there are ten people in the entire church it's unusual. I understand from talking to people at the church that the services on Sunday are pretty small also (relatively speaking).
I think Sacred Heart is the other truly "downtown" church, i.e. in the business district and located fairly far away from a residential area (although there are some new condos fairly close by). Acc to their website, they concentrate on homeless ministry and serving the hotel/convention trade. . . they're right at the end of "hotel row" on Peachtree.
I have no idea how many members there are at either parish or what their average Sunday attendance is - but IC is fairly desolate on weekdays.
I would say that that proves my point, except that you are right about the Shrine of the Immaculate Conception. Right now, Sunday attendance is growing, but the masses are never full. I think that is because the Shrine's "specialty" ministry targets gays/lesbians, and not a lot of other people have been drawn to that.