1. Supes' mom,

Superman's Kryptonian mom Lara was once described as being their equivalent of an astronaut.  That was later retconned into making her a scientist, supposedly on equal standing as Jor-El. Personally, I much prefered the astronaut take, and would push to bring that back.  Sure, she's dead either way, so it shouldn't matter much, but it kinda does.  Hear me out.

Krypton was supposedly extremely isolationist, which is why no other kryptonians survived the destruction of their planet despite being at a technological level where interstellar travel was possible.  This makes the character intriguingly tragic, as she must give up her own dreams of flying to other worlds.  It also adds a little bittersweet note to seeing her son be able to live the dream that she had to give up herself. 

I also like the idea that she herself was much like the early Earth astronauts, which were originally stunt pilots.  Daring, adventurous sorts, rather in contrast to the cold, analytical approach of Jor-El.  To me that means that she might have had a much easier time connecting with her son had she lived, since they both would share the same bold, adventurous streak.  That makes the impact of her death all the more poignant to me.  Yeah, it's a minor thing, but I'd love to see one story at least tackle with it.

2. Pretty much everything with Wonder Woman

Better villains is the priority.  Beef up Cheetah to global threat, or she is no match for a goddess. I prefered the Animated Series approach of making her a scientist over the whole 'cheetah goddess' deal.  I would love to see a take on her where she is played up as a Dr. Moreau sort who is trying to erase the boundary between beasts and humans.  It'd be extra cool if that meant she was the one who created Giganta.  Also, introduce some new villains.  Rogue amazonians separatists who once wore her uniform.  Demigods who wish to woo her into joining their side and bring the old gods back.  Demons, aliens, anything!  Also, if you're going to go the route of making her a child of Zeus... MAKE HERA HER ENEMY!

Her costume has gotten better over the years, looking more and more like a hoplite outfit.  Still, I'm sorry for the fans of her boots, but I would sooner go for something resembling the bronze shin guards that hoplites used.

Replace her invisible jet with an invisible World War II fighter.  Maybe the shapeshifting construct started looking like a pegasus, but after the death of Steve Trevor, the sadness of his death caused Diana to change it into his airplane in memory of him.  Kinda like how Snape's Patronus changed after the death of Lili. Spoilers!

Batman:

1. Bring back Cassandra Cain in some capacity, even if she can't be Batgirl again.

2. I.... dunno how to go about it, but I'm not a fan of Nightwing's name or costume.  It's actually not bad, to be honest, but it's nowhere as iconic as Batman's or Robin's.  It needs something to push it up to that level, but I'm not sure how to go about it.  Still, I'd set people to work on it as a top priority.

3. I've heard Scarecrow be described as being afraid of nothing, save Batman.  I personally think the character would be far more disturbing if he was actually extremely paranoid and neurotic, basically afraid of EVERTYTHING. But rather than having his fear make him meeker, it instead makes him more savage, seeing everyone as an enemy, and obsessing him with the workings of fear all the more.

4. I think Lock-Up should have become a classic Batman character by now.  The idea of an extremist anti-hero who wishes to capture and retain villains in his own private prison has a lot of potential. Not sure why DC never bother exploring the character further.

5. Make Catwoman more of a villain.  One who shamelessly and gleefully robs criminals in Gotham, and gets a kick of humilliating them and pampering herself with the spoils.  Sure, she kinda does that already, but the comics seem to focus more on her pursuits for her own brand of justice, rather than have show off her more selfish and greedy side.  In my take, she would still indulge in the occasional acts of self-sacrifice, but she's more self-serving.  Just like her better that way, and I'm in charge, so nyah!

Will continue in further posts.