One could argue that miners are investors. They invest in mining hardware in order to yield bitcoins.
Bitcoin doesn't need speculators and traders, but I also think speculation creates adopters. If not for the bubble in 2013, I may never have heard of Bitcoin. I originally bought in because of the hype, but now I'm a frequent user and not much of a speculator.
That's definitely in my definition of investors. Most people I know buying or trading, don't actually have bitcoin? They're just trading numbers on a screen, either as outright derivatives (futures maybe) or just "bitcoin balances" on trading accounts. These to me aren't investors, purely speculators. And you're right, they shouldn't be disregarded or dismissed. They do their bit for awareness, which then opens up adoption. Every participant has a role in this ecosystem.
So Bitcoin may have a hard time finding new speculators, or convincing old ones to keep speculating. But the miners, the users, these are the investors and they know to expect these dips, as they do the parabolic rises. Nothing changes.