It depends on the rules of the system. If the system arbitrarily limits the creation of hashcash to 2.5 per minute and limits the total in circulation to 21 M then it could be worth a lot (although with high volatility). Without such limits each unit of hashcash would be worth almost nothing, but the overall system might be more efficient and thus worth more.
Also, if the system limits itself to 7 transactions per second it may not be useful for anti-spam or bandwidth accounting.
But if this theoretical (but somehow very well defined) system supported offchain transactions, whereby a sender could attach a signed transaction for the appropriate amount to the sent message (rather than submitting it via a theoretical "peer-to-peer" network), then the throughput would be effectively unlimited.
This is really secondary to the actual real value these things would represent. Yes, they must be limited in supply, just as money must be - money would be useless if it grew on trees.
Your comment really only deals with the inflation rate of hashcash, which is a nominal thing and can be discounted in the presence of efficiency.
As I explained at more length in a comment on the post itself, the value of these things is a function of the dirty spammy goods they represent. To quote myself...
> Just as money is "stored labour", hashcash would become stored mail order viagra.
It depends on the rules of the system. If the system arbitrarily limits the creation of hashcash to 2.5 per minute and limits the total in circulation to 21 M then it could be worth a lot (although with high volatility). Without such limits each unit of hashcash would be worth almost nothing, but the overall system might be more efficient and thus worth more.
Also, if the system limits itself to 7 transactions per second it may not be useful for anti-spam or bandwidth accounting.