I love all the DC characters, and even the ones I am not super into have enough big fans that I wouldn't want to alter them in a way that would go against what makes them special to those fans.
That said, there are a few DC characters who I think are in need of a little help right now.
Wally is the main one who currently needs the most TLC, the rest are already being taken care of, like the JSA and Legion. With Wally, I would make him The Flash of Infinite Worlds, traveling the Multiverse in search of his family and having awesome adventures with a parade of alternate heroes like the Morrison's jeans & t-shirt Superman and more. That would give him a raison d'etre that is unique and interesting without feeling redundant now that Barry Allen is back.
Others are easy fixes like re-establishing Wonder Woman's WW2 history, by sending Steve and her back in time from the present to hang out with the JSA for approximately a decade, and maybe make a pitstop in WW1 so Diana's iconic No Man's Land moment can become part of her comics history. I would also sprinkle in a bit more of that Golden Age subversive kinky craziness that gives her something special.