"A flashy feature that has limited usability for victory."
Marvel's premier Cloak & Dagger organization, S.H.I.E.L.D., prefers to operate out of a Helicarrier. It's an Airborne Aircraft Carrier , and it's exactly as cool as it sounds. Unfortunately, it tends to crash. A lot. This typically causes about as much destruction as you'd expect from dropping something the size of an aircraft carrier from about a mile up, and usually has the inadvertent effect of releasing whatever superpowered psychopaths, alien viruses, etc. that happened to be locked up there at the time.
Helicarriers fall victim to The Worf Effect so often that in Secret Avengers, it is shown that S.H.I.E.L.D. actually has a sign counting down the number of days since their last Helicarrier crash.
The Cosmic Cube... you can do almost anything as long as you are thinking about it. Want D.C. to be a lake of fire? It will be, until you fall asleep. Then everything's back to normal and the heroes are kicking your teeth down your throat. In fact, anything you allow yourself to think about will take on some degree of reality and if you dream, that becomes real too. Even Doctor Doom couldn't handle it for very long.
Lampshaded by The Falcon at one point, who noted that the damn thing never works right and almost always backfires on whoever is trying to use it. He went on to suggest that there may be some Monkey's Paw-style karma involved.
Depending on the Writer, the suckers aren't actually that hard for alien civilizations to make. The Skrulls had one. Even us humans have made a couple. It's just a matter of learning the hard way that the little suckers are id monster factories, and then you don't make them any more.
The Ultimates for a while. A multi-billion dollar super-squad just sitting around because they caught all the bad guys? Well, rescuing people from a fire is cool but we got guys for that.
Of all of the Batsuits made, Jean-Paul Valley's suit during Knightfall fits this, especially the final variation. Massively flared out armored cape segments, built-in flamethrower, armor from head to toe. Can't fit through small spaces, easily ignite yourself from leaking gas and you gotta be superhumanly strong just to move around in that thing like you were Bruce Wayne himself.
Ironically, Jean-Paul would discover this with Batman's cape - long and billowy, but it has way too much drag. Dick Grayson, during his second tenure as Batman, would complain about the cape as well as it got in the way of his more acrobatic style.
Batgirl's latest costume have her a cap-like cowl that just slipped over her head. Nice, simple... easy to lose when you dive into the water. Even worse, it was 3D printed, which means it also suffers from the same things printers does.
A few of Batman's Batmobiles can be noted here as well. One of the Batmobiles he used when teaming up with Judge Dredd had its nose so tall that you couldn't even drive it realistically.
If Hank Pym is any example, turning yourself into a giant seems to be a rather impractical power for a hero. You never have enough room to move around, you're always in danger of breaking stuff or hurting someone by accident, and you're a target the size of a barn. Then again, if you're a villain who just wants to randomly smash stuff, it's pretty awesome.
Emphasized even further in The Ultimates, where it's shown that the very act of getting his costume on (which unlike his 616 counterpart, does not shrink or enlarge itself to accommodate his changes in size and thus must be stored in a nearby warehouse when not in use) requires several hours of preparation. If he wants to use his powers as a spur of the moment action, he has to do it in his birthday suit.
Adamantium. Sure, it's indestructible, but it's incredibly rare, prohibitively expensive, and almost impossible to work. You can't recycle it, either: Once it's been worked and set into a particular shape it can't be reworked. Oh, and it's highly toxic, too. The only reason Wolverine can even live with his indestructible skeleton is because of his Healing Factor, and the very presence of the adamantium in his body greatly impairs his ability to heal. Oh, and it's magnetic, so indestructible or not, it's pretty much worthless if you're up against someone like Magneto.
The toxicity thing only gets applied to Wolverine though, as several other characters have been laced with Adamantium without the benefit of an advanced healing factor (Bullseye, Hammerhead, Lady Deathstrike) with no ill effects. Occasionally handwaved by them taking medication to counter the poisoning. And in Deathstrike's case, the fact that she's not only a cyborg but one created at least partially by magic.
In an Archie comic story, one day an elf-like wizard appears out of nowhere and bestow on Archie a gift of "magic sneakers" that enable him to run at lightning speed (think The Flash). Yet none of Archie's friends are impressed; Jughead says that he'll just have to wait for everyone else to catch up when he gets to places first, and Betty scoffs at the whole thing, that one shouldn't be in such a rush all the time and stop to smell the roses. But Archie decides he really has no use for the sneakers when his chief love-interest, Veronica, refuses to go out with him because the speed would cause windburn and mess up her hairdo.
At one time, Spider-Man wore a special Spider-Armor to battle the New Enforcers when he found himself overpowered. While it did protect him, it was too bulky and it killed his legendary speed and agility. Later Spider-Armor were much more compact and allowed him to keep said speed and agility.
Mnemosurgery from Transformers: More than Meets the Eye. It's essentially a form of mind melding that lets the mnemosurgeon read and alter the memories of others. This is incredibly useful for interrogation, psychological warfare, and autopsy. Problem is, it's also insanely dangerous; one or two slip-ups can result in the surgeon frying their nervous system and surgeons sometimes "inherit" memories from their patients or autopsies, which manifests as severe PTSD and nightmares. The process is also addictive for the surgeons, meaning it can extremely difficult for them to stop performing. For these reasons, most mnemosurgeons die young and it's usage for anything other than autopsies is banned by intergalactic law, being considered a war crime.
The Marvel supervillain Razorfist is a martial artist/assassin who's had both his forearms removed and replaced with blades. This helps make him incredibly skilled and deadly in combat, but also means that if something happens to the blades he's helpless. He also needs personal servants to attend to basic hygiene and whenever he gets arrested, the blades are taken away and replaced with prosthetic hands to which he's never been able adjust. The character is the page image for Crippling Overspecialization.