But also so manga have the rule : new ability = even more side-effects.... eventually I started to dislike Allen for the fact that his only side-effect for having innocence is the fact he looks kinda creepy and that's all.
Almost all decent series have side-effects after using some super powers
One Piece : Whenever Luffy uses his 'Gears' he shortens his lifespan
Teknoman : Whenever main hero used 100% of his power, he lost some of his memories (in the end he got reduced to the mind of a child)
FSN : Whenever Shirou performs to powerful tracking spell, blades come out from his body which hurts him
Slayers : Whenever Lina Inverse uses Giga-slave, she is unable to move and her hair goes white
Claymore : Whenever one of Silver Witches uses too much of their power, there is a chance they will turn into monster...
Berserker : Whenever Gutts uses his 'Berserker Armour', his body gets serious wounds
Yu-gi-oh : Whenever Kaiba tried to smile, a puppy died
By see this - Allen does miracle power-up for the first time, making him on general level and there is no penalties at all....
Allen's "side-effects" mean that he's constantly hungry (you take biology, you should know!) and that his arm is extremely vulnerable to injury. Technically, all Exorcists have similar problems to the Claymore - if they use too much power, Bad Things happen (except that Exorcists experience extreme pain and possible loss of limb movement). Allen can use maximum synchronization (83%) without problems, but he still had to lose his arm and nearly die... multiple times. We don't know if the over-100% thing has any effects yet, but it probably will (and even if he doesn't, it's not only a pretty boring and ineffective power-up - generally - it's probably fairly easy to lose).
...Incidentally, do you see any vulnerabilites in manga like Bleach? =P
Bleach : Whenever Ichigo uses his hollow side, there is a chance he will lose it to the other Ichigo and become something hollow like...
Dragonball Z : Whenever they fight, they are extremely hungry - but come on, Kamehameha + Super Sayajin mode surely makes people hungry :D
Black Cat : Whenever Sven uses his eye, he loses lot's of stamin - and Train by using Rail gun puts lots of pressure on his shoulder
Chrno Crusade : Whenever Chrno uses his full power, the person he made contract with shortens her life
Death Note : Just by using Death Note, you close your doors to heaven or hell - moreover, if you make 'shinigami eye pact' you lose half of your lifespan
Code Geass : More you use 'Geass', less you can control it and it makes you unable to interact with other people.
Inu-yasha : While the main hero is invincible, Miroku can die whenever he uses his Kazana
Allen didn't died by using maximum of his hand - that's what pisses me off. It was Tiki who killed him. And moreover - this side-effect was just an excuse for getting new power-up and it seems it will be the same with Rinali.
The only series which I can't think off side-effects hero is Busou Renkin - but I never liked that series either.
None of the Exorcists DIE by using maximum invocation; it just hurts a lot and prevents further use of Innocence and affected body parts. Allen and Rinari died because of events after that (Allen by being murdered by Tiki, Rinari by experiencing air friction). Anyway, they probably SHOULD have died, so there isn't really a problem.
Also, you seem to be forgetting the constant energy-sapping effect. ._. Crowley was definitely feeling it on the boat, for instance.
And we don't know if any Exorcist has any other negative effects. Most don't seem to live that long, and this has only been going on for about a century. I'd think that risking your life every day and possibly being killed by your own Innocence if you didn't fight is a pretty bad thing, so maybe it's not fighting that has the bad effects... it's not fighting. How many of those manga feature situations where if a character doesn't fight, they die (and I don't mean because the enemy will kill them)?
(Oh, wait, Inuyasha does - if he loses his sword, he also loses his mind and goes berserk. Remember that? =D That's a pretty bad effect.)
It was implied in DGM that Exorcist needs to fight, because other way innocence will kill them. Suman's innocence killed him because he betrayed Order - he was to be killed one way or another.....
..and yeah, all of them has it - the situation where you fight or you just die because you didn't prevent it. It's the famous let's save the world theme which every manga has.
(..yeah, forgot about that :D)
School Rumble : Whenever Tenma wants to do something good, it works opposite to desired effect...
Yeah, if the Exorcists DON'T fight, they die. In the manga you've mentioned, the protagonists don't suffer if they don't fight (aside from the world ending and all that, but their weapons don't come and kill them).
xD Tenma. Well, not really, she's getting Karasuma.
Can't wait for 124. Lots of talking, but I guess that's okay. Apparently, Rabi gets a new seal.