The answer of this question is very simple.
If you're able to trade Bitcoin for anything else of certain value, then the value of Bitcoin is exactly that.
One thing I've come to learn from the conversations on this thread is to distinguish between value and price. Value is qualitative and price is quantitative.
Something is of value if it enhances the life of the valuer in some way. Water, for example, is of value to human life. We need to consume it at least every 3 days to survive (in hot climate the time period is shorter).
Something should be assigned a price ONLY if it is of value to your life. The price reflects the cost to acquire that thing from someone else and/or the existence of alternatives. So in a place where there are a variety of places to get water, then the price of water will be low. However, in a place where water is scarce, then the price will be high. The fact that the price is high doesn't mean water is more valuable, and the fact that the price is low doesn't mean that value has decline. It just means the costs to acquire it from someone else has change. The value (i.e., needing to consume it every 3 days to survive) remains the same.
Now, people can be mistaken or defrauded into thinking that something is a value when in fact it does not. And so they can be mistaken or defrauded into assigning a price to it when they shouldn't. This is why relying on the fact that others have assigned a price to something as a determinant on whether it is a value or not is not a good methodology to operate from.
Oxygen is very valuable for human life, but the price is free.
It's not always the case that something very valuable is very expensive.
Also value depends on the individual and the area they live
Some people value different things differently, and so on.
Basically there's no single price for something. Every person at different times value everything at different prices.
The markets try to get close to that real value with estimates, and people react accordingly.
