i regret that i sold my nem

That's too bad.
If you don't buy NEM now, you will regret again.
If NEM succeeds, I think 1 XEM=1-10 dollars, ofcourse it doesn't happen overnight, but building up a decent stash becomes harder and harder after each significant development/update.
To reach prices like this i guess we need about 5-10 years but indeed it is a realistic case.