The hard part about using the Chidori or Rasengan is making contact. If you make contact, the battle (should) be over.
I don't see how having a Chidori or Rasengan is that much better than just using a kunai. Sure, a Chidori does more damage; but still, if you stab somebody with a kunai, the battle (should) be over.
The point of Rasengan and Chidori is not just to make contact, but POWERFUL contact.
A kunai can never penetrate Gaara's shield or any other strong defences, but Rasengan and Chidori can. Oodama Rasengan and Rasenshiriken are on even greater levels because their damages are astronomical.
In the fight with Kakuzu, before Naruto came, it was incredibly hard for the others to stall out Kakuzu, let alone finish him. But with Rasenshuriken, the destructibility penetrated and annihilated his charkra system in cellular level. I don't think you can do that with a kunai.
The power of the Rasengan and Chidori is not limited to just "making contact". Charkra nature manipulation and shape manipulation comes into great meaning at this point: Sasuke can turn his Chidori into mini needles, arrows, sword (with adjustable length), and stream. Naruto can fuse his Sage charkra style into the Rasenshuriken to make it a flying disk of destruction. This can't be accomplished with a simple kunai.
Waiting "an hour or so" is neither a practical nor feasible option, especially considering the injured has that time to escape or heal or bandage their wounds, or worse yet, claim the upper hand in the battle. It would not be as easy as you claim it to be.
Not to mention that Naruto is full of ridiculously strong characters who can take a lot more abuse than one kunai stab and come out fine. Against enemies with that kind of durability or regenerative ability, the raw power of jutsu like the Rasengan or Chidori is absolutely necessary to secure the fight.
Saying that they're not that much superior to a kunai because you can wait "an hour or so" for the enemy to bleed out is like playing an RPG using only starter gear. It's not practical unless you're fighting the weakest enemies, and you're going to get quickly outclassed and probably killed by the first enemy that decides to wear armor.
Look, first of all, stabbing someone with a kunai does not instantly end a battle. Second of all, those two justus are very complicated and hard to master, even control. By themselves, you can do a lot of damage.
Rasengan is a dense ball of rotating chakra. A little chakra by itself is nothing, but if you harvest enough chakra to make a rasengan, you could so some serious damage. As your saw in Naruto Episode 95 (I think), Kabuto took a lot of damage when Naruto drove a Rasengan into him. See, Kabuto's cells can regenerate instantaneously, so it's pretty hard to do any damage to him.
Now, I understand your view on the chidori. All we really see Sasuke and Kakashi do with it is plunge it into other's bodies. But still, the chidori requires a user to be able to have advanced chakra control. Just like one of the variations of the Rasengan, the Rasenshuriken, the user has to perform a change in chakra to create the chidori. There are many variations of this jutsu that are better than the basic chidori, like the chidori blade. But still, the chidori itself is really strong.
In conclusion, I don't see why a Rasengan vs. Chidori would end a battle. Besides, massive amounts of chakra can be very reactive when making contact with other strong sources of chakra.
To be honest in early Naruto it (rasengan) seems to be more of a cool trick than anything else. It doesn't do that much more damage than a kunai and takes time AND a shadow clone to make. To its defense it does send the enemy flying and seems to be somewhat of a superpowered punch that can do some series internal damage, but from the complexity of its use and the time required you could throw 10-20 kunai in the time it takes to use it. Even though I do have to admit its a whole lot better when fighting stronger enemies, like in the fight with Kabuto. Against an enemy at that level a kunai wouldn't be able to do enough damage, but most importantly they could dodge or deflect them all.
In conclusion I would say that Rasengan, while a good technique to know for last ditch efforts against a superior enemy, seems to be a waste of chakra for anyone who isn't Naruto.
A side note for chidori, it seems to be a slightly weaker version of Rasengan. We see this when Naruto and Sasuke fight before Sasuke leaves, they both have similar levels of base chakra yet Naruto's attack does a noticeably bigger amount of damage to that water tank. Also from the type of damage dealt it seems fair to say that Rasengan was better at penetration. (as in basically a giant punch)
The rasengan is made of such violently rotating chakra that it sends you spinning violently in the opposite direction for a dozen or so meters or until you hit something. The first time we see the rasengan, Jiraya sent two guys spinning in the opposite direction and when they hit a balloon stand they destroyed it. Keep in mind only one of them got hit with the rasengan directly and the other was behind the one who was hit. When Naruto first used it Kabuto had started healing the impact point before he was even hit and it still knocked him out. As for the chidori it is stated to be a jab from a lightning covered hand that is performed at top speed, and considering Sasuke with the stage one curse mark dodged an attack made of sound, it's pretty fast. It's so fast that it gives the person tunnel vision and requires the visual perception of the sharingan to make it safe for the user to use it without being open to counter attack. The chidori/raikiri is aimed usually at the heart, so if you succeed in landing it, it's pretty much game over. Naruto managed to deflect Sasuke's chidori into his lung instead of his heart, and he still would have died if he didn't regenerate the lost organ and tissue. Considering the fact that we never see someone's heart get pushed out when they're hit with chidori, we can assume it's destroyed on impact. So no, I don't think that a kunai is as effective at ending a fight as the rasengan or the chidori.
In response to the other answers here, the rasengan is no joke. While using the rasengan for the first time Naruto one-shot Kabuto, even when Kabuto had started healing the impact point. Using the rasengan Konohamaru was able to take out the Naraka path of Pain and using a sage mode enhanced version of it Naruto was able to instantly take out the Asura path of Pain. Even after he had dropped out of sage mode, when Naruto managed to hit the Deva path of Pain he defeated him. As for the chidori/raikiri, the first time we see it used it would have killed Zabuza had Haku not intervened by sacrificing his life. When Sasuke used it against Gaara, he was able to break through Gaara's sand, something that was able to repel attacks from Lee, a major hard hitter. When Kakashi threw Sasuke into the water tower the chidori went right through it. When compared to what Naruto did, it doesn't seem all that impressive, but that water tower was made from metal, I would assume steel, which is much harder to pierce than the human body. In part two at the five kage summit he is able to use the chidori to pierce through the fourth Raikage's lightning chakra cloak, though he isn't able to pierce the Raikage's body. In short, the chidori and the rasengan are invaluable assets in a fight, more-so than a simple kunai.
