yankdownunder-
I know a bit about coin collecting.
There are proof sets that are rare and valuable and there are proof sets that are quite common and not worth much.
Coin collecting as a hobby is fun, but difficult to make money doing.
There are many, many unscrupulous dealers willing to take your money and sell you overvalued, overpriced and overgraded coins.
I recommend the PCGS site for info.
A full sheet of stamps or a corner block is worth more than an individual stamp if the stamps are collectible.
In the 40’s there was such a run on collecting full sheets of stamps that there are still many of some varieties available at approximately face value.
So as not to take this thread totally off-topic, if anyone is interested enough to start a coin-collecting thread I’d be happy to answer questions there.
I have only minimal knowledge of stamp-collecting.