While the value of old currency can vary depending on many factors, the simple answer to this question is, yes. Any bill that is no longer in circulation is worth a little bit more to certain buyers than the amount it originally was.
Currency collection has been a popular hobby since legal tender was first introduced. As long as collectors keep collecting, it will no doubt continue to be, so you should see any collectible cash only appreciating in value with time. Certain bills and coins are often appraised at high value with certain factors considered.
Rarity in circulation is the first and most important thing to recognize. Limited edition, memento or collectible sets with popular figure heads and are bound to be worth more eventually, simply because fewer were printed in the first place. The fewer copies there are in existence, the more valuable it is.
Age is also an important key in valuing all collectibles. Paper degrades over time and metal oxidizes, so the older the run of a note or bill is, the fewer of them are probably still in existence, and even fewer are likely to be in good condition. If you want to maximize the appreciation of value in your old money, it is very important to store it properly to ensure its condition is stable.
Rarity due to misprint is another factor that can make what would have been a semi-valuable piece turn into a super sought after treasure. Sometimes mistakes happen on the line in production of the currency, like an ink smudge, a flaw in the plates that causes inconsistency in printing, a print not being lined up correctly or a note that was cut poorly.
These mistakes can slip through the system and end up in circulation, unnoticed, before The Mint can correct it. These mistakes often sky-rocket the appeal of the currency. Make sure to have odd-looking bills looked at by a professional to see what kind of misprint you may have in your hands.
Lost or replaced types of currency will undoubtedly go up in value if the method of money exchange is entirely no longer being used.
Condition of the piece is the final quality of your piece to inspect. Simply put, the newer or more unhandled a piece is, the more valuable it is, especially with age considered.
Paper will eventually disintegrate into nothing without proper storage, so professionals have a finely tuned system for grading the levels of damage, so you can gauge how much you can resell it for with some quick inspection and comparison. The grading system is a scale from 1-70, where 70 is perfect condition. Make sure you take a good look at your old money to decide if you would like to sell it now, or look into better storage.