VIBRO: Vibro could be workable with a few minor tweaks. Firast: make his power work on any fault line. I see no reason why a power fueled by science (a machine gone wrong) would work on only one plate boundary. Heck their are other strike/slip faults in the world. I'd also play up the part of his origin where he got his powers trying to STOP earthquakes and be a hero. I'd use this, have him still see himself as a hero as he commits crimes. He may look like troma meets punk rock but he knows he got his powers and deformity trying to save lives.
CIRCUS OF CRIME: I have been thinking about this since the post a year or so ago saying how sucky they were. I'll drop my crazier ideas (such as a drear and humorless vampire clown competing for control of the circus and creating freaks to serve him) and get to the core idea I had.
The circus of crime is flawed because circuses are no longer seen as innocent fun. From elephants mistreated until they rampage to children being scared of clowns the circus has gotten a dark twist to it. Attendance of Circus's are dropping. So a Circus as a cover for a crime ring is destined to failure.
So what if Ringmaster and his Crew realize they have grown to love the circus and they are part of why it is failing. Instead of using a circus as a cover for crime they decide to use crime to fund their circus. They are still a circus that commits crime, but instead of using the circus for crime they use crime for the circus.
CORONARY: I think coronary did best with the creepy power to control peoples bodies. Having him regain this power is an easy fix. But if he is using this power to hold his shattered body together and now he is strong enough to hold himself together and use it on others does this mean he is very powerful if ever reunited? Yes, go with it!
ABSORBING MAN: both Absorbing Man and Wrecking Crew share a similar problem. They are simply blue colar thugs without higher education so this automaticly paints them as stupid, ineffective, and expendable. Creel is the luckier of the group as his relationship with Skeeter gave him some characterization.
Absorbing Man's biggest problem is how he gets defeated. Most of the time he panics and grabs (or is given) something weak and that stops him. The biggest advantage would be to have creel get over his panicing.
By the way, in Avengers Academy seeing the cosmic entities left creel so shaken I hope it ends up a character point with him.
WRECKING CREW: I think the previous idea of splitting up the crew that someone had has merit. It allows Wrecker to once again seem dangerous, Thunderball to use his mind, and maybe, just maybe Piledriver and Bulldozer to have a personality. (Piledriver inviting his son into the crew had potential for that but it was soon forgotten). Once they establish personality and become worthwhile foes reunite them. By then the crew will be known as something worthwhile and able to challenge Thor once more.
XEMNU: He mind controlled the ENTIRE EARTH except for the man who beat him. Remember that. This is among the mightiest mental powerhouses on this or any other planet. A major psychic threat who also has muscle to back up his mind. He is a hulking mental terror. Show him as one.
Granted, in some respects it would be a complete ripoff of the Batman Returns movie, but why not turn the Circus of Crime into a Circus of Fear?
Play up the demonic clowns, tortured undead animals, sadistic ringmasters, fire breathers who breathe fire at their victims, knife throwers who use people for target practice, lion tamers who use their whips on humans, sword swallowers who kill people with their stomach contents, lobster men and bearded ladies who use their unique appendages to kill people...
To keep it from being a complete Batman ripoff, put a supernatural spin on them and make them Ghost Rider, Daredevil, or Sleepwalker villains.