The $10 bi-metallic Library of Congress coin does currently have a unique place in US numismatics and will likely always have a collector following. As far as its investment potential, it's harder to say.
The market for modern US commemoratives is not a strong one at the moment; many coins are selling for far less than they were a few years ago. That said, the current market does offer a number of buying opportunities with potential strong upside.
Back in the summer of 2012, the LoC coin was listed in the very reputable Coin Dealer Newsletter ("The Greysheet") at $4,200 in Uncirculated. The most recent completed auctions on
ebay for uncirculated examples (including MS-69 and MS-70 coins graded by PCGS and NGC) show prices between 30 and 45% of the 2012 level. So, if you bought the coin a few years ago, you would likely lose a significant amount of money if you went to sell it today.
IMO, a buyer of the LoC coin at today's prices has very little downside risk. When gold and platinum start going up again (as they certainly will) the market value of this coin will also rise. Will it go as high as $4,200? Who knows, but it's certainly possible if a new batch of collectors begin seeking a complete set of modern US commemorative coins.
Good luck! Let us know what you decide.