The aisle situation actually isn’t in bad shape. I tried to make it evident in the photo that the air supply is dumped in front of the racks and the return is behind and above them. It’s not a bad setup for the small multi-purpose closet we have to work with.
There are temperature sensors mounted in the hot and cold aisles that read about a 17* F difference, which doesn’t seem bad. Although the two racks don’t span the entire width of the room, they do obstruct nearly half of it. Adding some additional obstruction to improve the separation between aisles isn’t a bad idea of course, but considering the filing cabinet and other things that need to stay in there and the fact that it’s already tiny and cramped to move around in, it’s not practical to add a lot. Maybe just on the left side.