dvdivn given ethereum's difficulty rise (forced by iceage feature) ethereum is not going to give you a ROI on a rig at this time. That being said, like most crypto, while we plan for the now (purchase rigs when its high return), the people that have always benifited kept running rigs on different currencies during the best and worst of times. For a long time last year, ethereum, even with low difficulty was not profitable for most people mining it, however that was at a $6-10 USD ethereum price. People that kept investing in power cost to keep the rig running earned 100-190+ ethereum from July of 2016 through March of 2017, where the huge rise paid huge dividends on a 2500.00 rig.

Moral to the story is mining is an activity where you are exchanging power/hardware for a token, of which could at some point become very valuable as normal supply/demand dynamics work/play. There is always a risk it could go down substanially and/or a improvement plan (EIP for Ethereum, BIP for Bitcoin) can make an alteration that changes the proverbial game, however, history has shown nomatter what, value has increased for most all of the active developed cryptocurrencies.

Litecoin, Dash, Ethereum, Bitcoin, Monero, Namecoin, ...essentially every crypto has benefited from the continued exposure and advancement of the sector. Mining is a way to hedge that growth and be left with something tangible (hardware) that still remains to be worth something (GPU's / hardware still has other uses, there by can be solid to recoup some of the cost)