Hey National, 

In what terms do you ask by optimal "value"?  My assumption is your asking the GRT conversion back to USD...  With that assumption, my opinion is that no one can predict where any of these digital currencies will be 10 - 15 years in relation to fiat.  I personally don't think in terms of the currencies related back to fiat because after the 2008 crisis I don't believe the fiat currencies will last much longer with trust of the people. 

So to answer your question the value of 1 GRT will always be the same value of 1 GRT today, tomorrow, and ten years from now.  All that will change is what that 1 GRT will be transacted for, the utility of the currency.

This is one of the biggest challenges that face the crypto currency demographic is they look at these currencies like investments in relation to USD or other fiat, this is why you see all these pump and dumps with greedy individuals trying to make a quick buck.  Even LTC recently went through a pump and dump...

It'll take some time but when GRT plugs into the specific markets that are being targeted it will be a special currency to be apart of . 

Cheers,

Brandon