Will my coins increase over time?

I get asked this question quite a bit.  A person either collected coins or they received them as an inheritance, and they want to know f the timing is right to sell their coins.  First off, the coin collecting market is getting smaller not bigger.  There are fewer and fewer new coin collectors interested in coins.  Coin collecting seems to be a thing of the past.  Now I will say that there are exceptions to every rule.  There are certain coins that will always be worth a ton of money because they are extremely rare.  But take a common dated circulated wheat cent, a coin the has over 100 million minted.  It really doesn't matter how long you wait to sell that coin, it's not going to appreciate.  A coin is going to appreciate based on supply and demand, its simple economics.  If there are a lot of collectors interested in adding a certain type of coins to their collection, those coins may increase in value-as long as the activity and interest levels remain steady.  In one of the coin industries pricing guide shows if certain coins are trending in one direction or another, by a red or green arrow next to the price.  I will say that lately we see more red arrow than green arrows.
However there are coins that may increase based on the composition of the coin.  An example would be old junk silver coins that are made with 90% silver.  At the time of this writing silver is trading at about $24 per ounce.  Well logic says that if silver goes to $50 per ounce, the silver coins that people have are going to more than double.  But we are dealing more with the investment side of gold or silver.  Gold and silver can go up or down and a minute by minute basis.  I am often asked to predict the future!  I really have no idea what the future prices of gold and silver are going to be, but I have been around long enough to know certain indicators.  Also, when a person has a smaller collection, say it's worth $2500.  If the value of gold or silver goes up 4-5% the impact is fairly small.  However, if the collection is $250,000 a 4-5% can add quite a few dollars to the bottom line.  I would say this is one of the bigger differences between coins and stamps or sports cards.