Bitcoin mining is now serious business.

You will have to keep making sure your miners are running correctly, and after some time you'll have to upgrade to the more efficient ones. Also, difficulty keeps going up, so it's always harder and harder to hit a block. You might be able to get more bitcoin in the long term, or maybe not. But work will have to be done regardless.

It's a personal choice, but if you just want to invest, probably buying Bitcoin directly is the right answer for most people as you won't have to do the mining work.