Blockspace isn't that important, actually. Many people believe that a smaller blocksize would actually be a lot better. What really matters is the Lightning Network which will allow for thousands of small purchases per second, even moreso than VISA, Mastercard, etc. This is what we truly need. 
Actually your wrong. Blocksize determine how many users can use Bitcoin. To be able to use Lightning Network, exchanges or other offline systems where you can do potentially unlimited transactions, you have to move Bitcoin first there - and this is very limited resource, thats why no much more people can use Bitcoin anymore.
Is btc destined to become basically sovereign wealth? / store of value, which I admit is a massive killer app.......?
Yes, it is already becoming something like that. Mainly a store of value/digital asset which keeps growing in price.You mean just speculation based asset, which is pretty bad at keeping value over long time periods.