I think its always been a good decision to buy ethereum. The earlier you buy the better. You should buy now because ethereum is one of the most reliable altcoin out there. Some even predict it will surpass bitcoin in the future. Considering its value now and the trends, I think it will continue to increase its value in the near future, probably reaching around $2000 at the end of 2018. So its a good investment to buy ethereum now. But of course its more productive if you invest in different altcoins, not just ethereum, to maximize your profit.