I think many people (newbies) think the value of Bitcoins can only go up is because they know there will never be more than 21 Millions Bitcoins on this planet. Bitcoins are scarce compared to the 7 billion humans on this planet or the trillions and trillions of USD and EURO in the financial markets.
What they forget is that you can, almost indefinitely, divide a Bitcoin. In milli-Bitcoins (mBTC), micro-Bitcoins (µBTC) - or Satoshis (0.00000001 BTC). So there’s plenty of Bitcoins left for everyone on this planet. Or Satoshis (300,000 Satoshi for every human to be exact).
By that logic, 300,000 satoshi could potentially represent the life savings of the average person. That being the case, how much would 100,000,000 satoshi (ie, a whole single bitcoin) be worth? Unless you think the average person owns less than $3, it's obviously more than $1000.
As long as Bitcoins are not used in "real life" (e.g. I can buy stuff from Amazon or pay a pizza with them) they have zero value. OK one could say they have at least the value of the electricity that has been used to create them.
One could say that, but one would be wrong. Hiring a bunch of people to dig a hole in the ground and then fill it up again costs money, but it has no value.
But on the other hand no one measures the value of a 100 Dollar note with the paper and the ink that it's composed of. A 100 Dollar note has it's "value" because it's accepted everywhere and I can get "stuff" for it.
Bitcoins are accepted almost nowhere – hence their "value" is pure from speculation. It can be 50cent today, 50 USD in a month and 10cent in two month. No one should complain if he has lost money. We have all seen this before. In the 17th century in the Netherlands: The Tulip Mania.
"Almost nowhere" is not the same as "nowhere". As long as bitcoins are accepted
anywhere, they have value there. To use your example, A 100 dollar note is not, in fact, accepted everywhere. Supposing it is a U.S. 100 dollar note, it will not be accepted in Europe. An Australian 100 dollar note will not be accepted in the U.S. But that doesn't mean it has no value: you can go to a bureau de change and exchange it for whatever currency
is accepted. In the same way, you can exchange your bitcoins for local currency at any of the numerous bitcoin exchanges. As long as someone, anyone, accepts bitcoins, they have value.
The real question is
why should anyone accept bitcoins? Simply, bitcoins enable instant payments anywhere in the world, any time of day, any day of the week, with no restrictions, for far lower fees than any other payment network on the planet. If you're looking for the "instrinsic value" of a bitcoin, there it is.