Most American banks aren't building those kinds of buildings *now*. I think they stopped doing that in the 50s. Seeing that kind of building implies they've been around a long time. I don't know if it was considered over-spending when it was done. It was a more common thing to do in the early 20th century. It may have been a kind of reassuring message to people who grew up in the Depression. A "we're here to stay" expressed in architecture. Banks also may have been in competition at that time to pull in well-heeled customers who didn't want to be seen going into a shabby building. People cared about stuff like that back then--guys wore suits all the time, and Fedoras with the suit as they were meant to be worn, with no hint of irony.