But that's precisely what currencies are largely valued on - the value of transactions conducted in that currency, and the speculative direction of those transactions.

Why do you think the US dollar is a stronger currency than, say, the Pakistani rupee? The US dollar is used to pay for more transactions AND speculators make a directional bet that the Pakistani economy won't be as robust as the US economy or that the US dollar's hegemony won't be threatened in the short-term.

If you have a speculative belief that Ethereum will power the digital economy, it is reasonable to value it at XX price.