I think the value of NEM will depend on a number of factors: 1)what kind of innovation we'll be able to deliver, 2)how well we'll market that innovation, 3)what kind of active community we'll be able to build, 4) how rich of an ecosystem we'll be able to offer and more importantly, how simple we'll be able to make it for the average user to gain access and use all this.
That being said, I expect one stake to be at least 5-10 btc after launch - at least 10-15 btc after 6 months - and at least 15-20 btc after one year. Please note that I'm very conservative in this projections and think there are reasonable scenarios where the value could easily be double from the one I mentioned.