Firs tof all, Waves holders will receive Vostok airdrop, so there is a direct benefit for Waves holders. Secondly, Sasha explained that Vostok will be a addition to the Waves platform.
Fair point. And we should not forget that Vostok tokens will only be bought with Waves for non-institutional investors. As the Vostok website says, Vostok tokens can only be bought with fiat when investment is >= $500k, otherwise you need to invest with Waves. For that reason normal investors will acquire Waves to invest in the ICO what however will very likely cause in a price surge.