Random Question As To When Coins Increase Value Due To.

Value is based on 3 things, rarity, collectibility/demand and condition.

As an example the 1909 S VDB is not rare by any means, but it's in demand and high grade coins are very much in demand, hence you have a very expensive coin.

I have a coin from Portugal that maybe only 100 exist, it's also high grade but very little demand so I paid under $100 for it.

What can happen is that bubbles can form. For example, Peace dollars were looked down upon compared to Morgan's which meant that one could do the Peace dollar in AU (1921 to 1935) for about $600/$700 in 2019. In 2021 with the release of new Peace and Morgan's the demand for Peace dollars went up thereby increasing the prices. The Peace dollars aren't rare but they are in demand hence the price increase.

So to answer your question, yes coins can go up in price and can also go down in price.

It's an interesting question.

For the British royals, remember that there are no official coins with William and Kate on them until they become king and queen. Maybe there will be medals struck to honor this event, but these are not coins.

Charles is not a terribly popular chap, so the only way his coins will be valuable is if the mintage is very low.

As for U.S. presidents, I guess you could see what the Presidential dollars are selling for on ebay to get your answer.

There were UK coins issued under QEII that had other royals: many of the crowns. Also don't forget the Churchill crown. You don't have to be the ruling monarch to be honoured on the official coinage.