The Smithsonian Paradox

I have a feeling this will be a disclaimer-rific essay.
Many years ago someone once told me that to spend 30 seconds at every exhibit in the Smithsonian would take longer than a person lives. In effect, if you started as a child, you could live your entire life looking at things in the Smithsonian, and not finish it before you die. That's all well and good, but that got me thinking about what if someone actually did that. At the end of their life, they would know a great deal and have nothing to show for it.
At what point does learning cease to be practical?
In what I perceive to be a popular movement nowadays (1 disclaimer), there is an effort to attack 'common sense' concepts with new ideas. A great example of this is the book 'Freakonomics' which details similarities between crack dealing and McDonalds management layouts, or a potential correlation between Roe vs. Wade and the drop in the crime in the early 1990's. It hinges upon people from different disciplines coming together and applying what they know to scenarios outside their expertise and finding commonalities.
Another example comes from 'Blink', where Gladwell describes the meeting of NY stock exchange money managers and 3-4 star army generals. Apparently one guy had a mixer and invited the two groups, and they got along well, merging discussions of military strategy and rapid decision-making on the trading floor.
I enjoy reading these books and find them very enlightening. I'm working on one right now that parallels Navy Seal teamwork into better business models for project management. But all of this hinges on me actually being able to put this stuff to good use. At what point do I put the book down because it is of no practical use for me? At what point is edification not worth my time, at what point is it a waste of my time?
I'm a big Godzilla fan, as evidenced by the picture of airflow around a Godzilla in a wind tunnel. I can probably recite all of the enemies he has faced in under a minute. I can detail how many times a given enemy has appeared in different movies, and cite style changes from movie to movie. I have gathered this knowledge, spent time and money in so doing, all the while knowing that it serves absolutely no practical purpose. The collectibles have a certain monetary value, but they will not appreciate like a CD might. This knowledge will not improve my odds at a job interview, nor was it of any use when I was dating, as my wife will attest. All in all, it's amazing she didn't run out of my apartment screaming the first time she saw my shelves of snarling Japanese vinyl.
In the morning I often hear sports statistics being quoted over the radio. This is one much closer to many of my non-readers. I'll hear many conversations at work about baseball teams, football teams, particular pitchers, hitters, quarterbacks, linebackers, centers, etc. "Sure that guys 3-0 for the last three games, but that doesn't mean anything!" "Doesn't mean anything, how can you say that?!" "The next game is in a dome, we all know that throws him off." "That's just a rumor." etc, etc etc etc. Not to knock sports enthusiasts (2 disclaimers), but this information serves only to fill the quiet spots when people might wish to think, or pursue other topics in greater detail. Unless you are gambling or a player yourself, it is effectively useless.
How much time do we spend gathering knowledge that is useless to us, and why? Do we acknowledge its uselessness and gather it instead hoping to make one of those bizarre connections and write a popular book about it? Does the marine biologist who loves waffles hope to someday make that mysterious link between wafflemaking and algae blooms? Does the computer forensic expert/car enthusiast hope to understand why Corvette thieves prefer the classic Mac OS over OSX or Windows?
I can appreciate an 88 year old woman going back to school to get an accounting degree (3 disclaimers!), but I have to stop and ask why she feels that's the best use of her time.