In the last few years of my active and drastic moves towards Bitcoin, what I have come to understand with Bitcoin is that, no matter how little your portion is, it drives its own units interest and likewise loses if when the Market either go up and down.
My few Bitcoin investment done using my leftover and other extra cash in two years ago have yielded enough interest and now I comfortably own my own home through my Bitcoin this is exciting time for all the Bitcoinairs and knowing that after achieving a milestone we still have some Bitcoin waiting for the next big opportunity.
There's no small amount for bitcoin. Whatever amount you have, the fact that it's an extra money, don't hesitate to invest.