Currency "investors" are always speculators; they are not buying a productive asset of any kind.
This is misleading, in the sense that currency is a very productive asset. It doesn't produce more currency (unless it is a staking vehicle) perhaps, but that is almost a tautology, content-free. It enables the whole economy of that currency. Calling that non-productive would imply that all economic activity was non-productive.
Were there no efficiency and growth-enabling features in a new technology (currency or otherwise) it would fail to thrive in a competitive landscape. An investment in a novel currency is an investment in the whole economy of that currency. It adds capital to the economy, which helps it to achieve a productive critical mass, and the growth of that overall network is what the investor is betting on. Because it is an investment in the totality of the economy, it is maximally diversified, relative to that economy - sort of like indexing on steroids. The whole world becomes your productive asset.
We're getting off topic. Little to none of that goes toward development of the core technology. If you want to directly support development you have really only three options. Develop yourself, pay someone else to do specific development, or donate to the project.
Not directed at you personally, this applies to anyone.
Also, the "economy of the currency" for any cryptocurrency but certainly for any non-btc cryptocurrency is essentially all speculation, so we're back to investment = speculation even if we agree it is an investment int he whole economy.