This is the price of SBD vs Bitcoin over the last month, it vaguely follows bitcoin but it's clear to see it's doing it's own thing; I don't think it's price is driven by investors as much as other crypto's, it's a lot more driven by users from what I'm guessing, which is a good thin (at least in my opinion).
And you are right, users don't have to buy their way into the platform, but after being here for a while, the temptation becomes too great for those with money to spare.