JOEL - I would not consider President Hinckley's response in 60 Minutes to be an official statement on caffienated soft drinks. He was giving a simple quick response to a larger list of things that were mentioned in the question.

Mike Wallace: No alcohol, no tobacco, no coffee, no tea, not even caffeinated soft drinks...
Gordon B. Hinckley: Right.

I am sure, however, that in his personal opinion caffeinated soft drinks should be avoided as well. I have heard that story about Elder McConkie myself a long time ago, and I'm not sure if it doesn't belong to the "Mormon Urban Legends" category.
But, even if the story about Elder McConkie were true, he may have only been expressing his own personal opinion about it. In the Book of Mormon Jacob warns us of the danger of looking “beyond the mark", like those who adhered to the law of Moses in such great detail that they failed to recognize the Messiah whose coming had been anticipated (Jacob 4:14). However, based on things that others have said and even though there has been no official statement from the Church on the matter, I do not think abstaining from cola drinks should be considered as looking "beyond the mark".
Consider the following statements:

This came from the office of the First Presidency in a response to a letter they received in 1972. The answer came from Elder Joseph Anderson, Secretary to the First Presidency:
"Your letter of April 22nd addressed to the office of the First Presidency asks for information regarding the Church's attitude pertaining to the use of cola drinks, particularly as it pertains to the Word of Wisdom...I am directed to tell you with reference to the cola drinks that the Church has never officially taken any attitude on this matter, but the leaders of the Church have advised, and do now specifically advise, against the use of any drink containing harmful habit-forming drugs under circumstances that would result in the acquiring of the habit. Any beverage that contains ingredients that would be harmful to the body should be avoided."

From the Encyclopedia of Mormonism:
"With the appearance of cola drinks in the early 1900s, the Church was confronted with cold beverages containing caffeine, a harmful substance believed to make coffee and tea unacceptable. While no official Church position has been stated, leaders have counseled members to avoid caffeine and other addictive chemicals."

President Howard W. Hunter:
"Live the spirit of the Word of Wisdom. We complicate the simplicity of the Word of Wisdom. The Lord said don't drink tea, coffee, or use tobacco or liquor and that admonition is simple. But we confuse it by asking if cola drinks are against the Word of Wisdom. The 89th Section of the Doctrine and Covenants doesn't say anything about cola drinks, but we ask questions that go beyond the simplicity of the lesson that has been taught. We know that caffeine is taken out of coffee and used as an ingredient of cola drinks. It seems to me that if we really want to live the spirit of the law we probably wouldn't partake of that which had been taken from what we were told not to drink." (Teachings of Howard W. Hunter)

So according to President Hunter we should try to live the spirit of the law and avoid any drinks containing caffeine. It seems that common sense and living the spirit of the law should also include not being fanatical about it as well. If there are other things to drink besides cola, why not drink them instead? But, if I were dying of thirst on the desert and the only thing my rescuer had to offer me was a Coke, I would drink it.
Drinking a cola won't prevent someone from being able to go to the Temple or even the Celestial Kingdom, but we will be blessed in this life according to how faithfully we follow the commandments of God and the advise of the Church leaders.
We must also learn to trust our own judgement and personal revelation on many aspects of the Gospel such as this.

"For behold, it is not meet that I should command in all things; for he that is compelled in all things, the same is a slothful and not a wise servant; wherefore he receiveth no reward." (D&C 58:26)

I do believe this is a personal choice that everyone must make for himself and we shouldn't pass judgement on others who decide to choose differently.