I can agree with you that a bitcoin unit was not first a good before it was declared a money and therefor has no inherent value as a commodity. I don't think the order of events matters very much. We could have a money and then discover that it's a wildly useful commodity. But the bottom could always fall out (just like fiat) if it's utility is solely based on its use as a money.
I agree that type of object can be exchanged and have an exchange value prior to a discovery of a direct serviceableness (Bitcoin is an example of this). However, I do not believe that such a type of item will, prior to it becoming a directly serviceable good, become more widely adopted than already existing directly serviceable commodities that have already been used as money for thousands of years. I also do not believe it would gain any adoption at all in the first place without the first adopters either misunderstanding the concept of money, or intentionally deceiving others in order to acquire valuable goods from them in exchange for worthless items.
I think your emphasis on the ledger service is the correct perspective. But why don't you see the service as inherently valuable? There exist similar services in various shapes and sizes, but no service has the unique set of properties including a momentous network effect, that bitcoin currently enjoys.
The value of the ledger service is dependent on whether the type of object the ledger is capable of keeping account of has a market value.
If a potential customer recognizes the type of object is not a directly serviceable good (a plain number that does not represent an actual good and has no other special meaning or interpretation) and no one else is willing to offer any goods for it, and they don't expect anyone to, they will have no reason to acquire any themselves, and the ledger service will have no customers as it is of no value to them (it is worthless, just like the numbers it keeps account of).
If a potential customer believes that they can benefit in some way by having a larger number in their account on the ledger, they may choose to offer goods to increase their number. Because they believe they could benefit from having a larger number in their ledger account, they then value the ledger service.
Bitcoin may be a horrible storage of value (arguable), an unreliable unit of account (volatility makes this true), but the system provides a revolutionary exchange of value. So, perhaps today it does not act as money, nor is it a physical commodity. But if you will allow for a new coined term (pun intended) bitcoin transactions are already a valuable fungible "service commodity", from which we can hope the other properties of money will emerge.
What do you mean by "exchange of value"? My understanding is that people exchange goods, not some abstract concept of value.
Bitcoin transactions have no value without "bitcoins" having an exchange value, as the only thing normal Bitcoin transactions can metaphorically be used for are to "send bitcoins to someone's address". If no one was willing to exchange any goods for a "bitcoin", there would be no value in creating a Bitcoin transaction, and the whole Bitcoin system in it's current implementation would be worthless.