In 20 years, I think 30 BTC may be enough for retirement, if the currency continue with a good level of appreciation and adoption, of course.
I think we could not predict the future, so probably 30 BTC might not be enough.. It is better to have plenty...Bitcoin I think should not be our only retirement fund, there should always be other alternatives just in case bitcoin fails, but one thing is for sure, fiat would not fail, and other investments in real life like real estates...