In my experience mining as speculation is the best way to do it. Find the new but unknown coins to mine. For example i mined 800 stratis on the last day of their very short POW stage to get the coin going. From one day of mining That is now worth about 10k usd. This also led me to research stratis and buy in early.
Also mined deeponion in the first few weeks (absolute scam garbage coin) but i was able to sell those coins for well over 1k several weeks later.
Other than that mining is good for a certain kind of stability that trading cant offer. Im sure eth miners that have stuck it through even in the times of low roi are all probably doing pretty good.
All that being said, as you have discovered investing in a coin instead of in mining hardware almost always will be the better choice long term, unless you have a very efficient setup and a solid business plan.
Also POS is the future for efficiency/economic reasons, mining will eventually be (or already is) an environmental hazard.
Thanks for writing in. It is funny that you mention finding cheap undervalued coins that you can mine in the early stages that will grow exponentially a short time later. This is the exact same philosophy that I had which led me to dual mine Decred and Ubiq. Both of which have grown exponentially over the past few weeks.
https://steemit.com/cryptocurrency/@roadsuntraveled/the-joy-of-printing-money-my-start-in-cryptocurrency-mining-and-finding-the-best-coin