Correction: ignoring speculation, the base asset-value of bog-standard crypto securities (i.e. the ones that don't "do" anything other than get traded around) is sustained by a mix of:
• capital flight (in countries where the routes for regular ForEx conversions have been restricted)
• financial "regulatory sandbox" instruments development, i.e. the ecosystem built on "security tokens." (This, as it turns out, is mostly being built out by the existing financial sector.)
• grey- or black-market purchases — i.e. purchases illegal for either the buyer or seller according to their local jurisdiction. (Which doesn't usually mean criminal activity as you'd think of it, but rather is most often a routing-around of brain-damaged legal codes, e.g. FDA bans of non-dangerous drugs. I have a friend who's trans, who found it impossible to get prescribed hormones where they live — but got them easily on the dark web! Another friend, who had gone through every step in the workflow to solving their chronic illness and come up short, used crypto to buy a Russian medication that doesn't exist domestically, and it solved everything for them. Etc.)
• facilitation of trade in environments with untrustworthy civic financial infrastructure, e.g. Venezuela
• facilitation of trade between private citizens of countries that actively attempt to prevent trade with one-another, e.g. countries who have trade embargoes, or even countries who are at war
Note the common theme: cryptocurrencies enable people to enter into trade with one-another when one or more governments don't want to enable that trade, or even want to actively prevent that trade. That's the "base value" that speculation on cryptocurrency is a multiplier on top of. Cryptocurrencies route around embargoes/tarrifs/etc. in the same way that the Internet routes around downed links.