I definitely see where you are going with this. I would argue that the developers did not originally balance the intimidate system very well, and that the intimidate rules are not well thought out. What you have is a character that can often finish combats before they should be able to, and although it makes sense in some scenarios it is clearly abusable. Many players have dailies that can hit a group of baddies with a condition for a limited time, but here we have a skill check can remove several bloodied foes from combat.
The rules for intimidate use a skill check against a defense, and the result does not work well. A level 4 character with the appropriate feats and items succeeds on a 4+ where a similar character trained in intimidate but not tweaked for the skill needs maybe a 15+ or higher. There is too much difference. If intimidate were a real issue in my campaigns I would rework its combat use as an attack. This would cause it to scale and balance better by level, and make it more accessible and well explained.
I think a target roll of 16+ (25%) to force a bloodied enemy to surrender is fair for a character trained in the skill, and with a decent starting ability score (16). Such a character has about a +5 bonus on this check at level 1, and monsters tend to have defenses around 13 at level 1, if the DMG is to be believed. Thus a fair target DC is the Will defense + 8. If they hit the defense, but not at +8, they still get some effect. They can also have an effect on non-bloodied foes.
Intimidate foes: at-will, standard action, fear
Close Burst 5
Target: each enemy in burst that can perceive you
Attack: Cha or Str vs Will
Hit: The target is demoralized. It gains a -2 morale penalty to attack rolls and skill checks (save ends).
In addition, if you hit the target's will defense +8, and the target is a minion or bloodied, the target surrenders. It will not act as long as you continue to focus on it. If you attempt to bind the target it will allow you to and if you direct it to go somewhere it will obey. If you or your allies attack the target or you continue to fight other foes, the target will flee. If a fleeing target is cornered it will resume fighting.
Miss: You gain a -2 penalty to any further attempts to intimidate the target until the end of the encounter. This penalty stacks.
Special: You gain a +2 bonus to the attack if you are trained in intimidate, and a further +1 for taking skill focus intimidate. If you are wearing a magic item that gives a bonus to intimidate, you gain an enhancement bonus to this attack roll according to the level of the item (+1 for level 1-5, +2 for level 6-10 etc). If more than half your team is bloodied or dead, you get -2 to the attack. If more than half of the opponent's team is bloodied or dead, you gain a +2 bonus to the attack. Elite monsters gain a +2 bonus to their defense for this and solos gain a +4 bonus.
Under this system, a level 4 (+2) character with 20 Cha(+5), trained(+2), skill focus(+1), and a Circlet of Authority (level 7 = +2) would get +12 to this attack. A level 4 enemy with a Will defense of 12+level = 16 would be intimidated on a roll of 4 or higher or would surrender on 12 or higher. A level 4 (+2) character with 18 Cha (+4), trained (+2) would have +8 to hit, intimidating on a roll of 8 or higher, and forcing surrender on 16 or higher. To me, this seems more balanced. Min/maxing will increase your ability to intimidate, but not to ridiculous levels. Not min/maxing will not make it impossible for you to intimidate.
Under this system, racial/background bonuses do not affect the attack. I did this because racial bonuses never give a character an outright bonus to an attack roll, and because any race that gains a bonus to intimidate already has an attribute bonus for Str or Cha anyways.
To help flesh out and balance using intimidate as an attack, I suggest letting diplomacy be used to cure demoralization/surrendering like a heal check.
Inspire allies
Action: minor
DC: 15
Success: Each ally within 5 squares can make a saving throw against being demoralized by an intimidate attack or surrendering because of an intimidate attack at a +2 bonus. On a success they are no longer demoralized or surrendering.
Failure:You cannot try again until next turn.
This way, if your players get intimidated by the monsters, they have an option not to be TPK'ed.
Anyways, have fun with your character!