I still benefit from censorship resistant transactions if no new participants join.
I still benefit from psudonymous levels of privacy if no new participants join.
I still benefit from the strength and security of the network if no new participants join.
Because the network itself is a tangible resource. Real people running software on real devices. Ensuring that every single transaction in every last block conforms to the rules of the protocol. All of that infrastructure exists. And you need bitcoin (the currency/asset) to benefit from Bitcoin (the network). The value is real and it's only the willfully ignorant who are unable to see it.
Also, we need to realize that if you have no dollars, then you are getting it from someone else? I mean is that the same logic? Or gold? The person who got in the first, made all the money and the one that got the last will end up with the worst situation?
This ponzi scheme thing is trying to get into everything but we all know that it is not the reality. Sure you could end up with a ponzi scheme somewhere, they are still out there but to call bitcoin a ponzi scheme, that is just a comedy. We get to use it as well, we get to earn it as well, we get to spend it as well. To think just because there are investors, and hence why it must be ponzi to make everyone rich, makes gold a ponzi.