They have more value because they're proven players. That doesn't mean they should be traded instead of a prospect.
Both Nyquist and Tatar hold much more value in a trade right now, Pulkkinen is out-producing both of them in their respective minor league careers, and Pulkkinen is that coveted right handed sniper we've been longing for...
Production in the minors doesn't guarantee production in the NHL.
Who is "we?" I haven't been longing for a rh sniper.