I also considered mining, which could also be considered as an investment, but is usually controlled by ones with the highest hash rate, and hence seems like the need of having a large number of computing units (cpu,gpu,asics) to be successful.
You can still mine some altcoins if you have a higher hash rate miner but it all depends on all of your expenses in the current and the total rate that your miner can give to you. But since the difficulty level is raising it must be harder and harder for someone to mine when he got too small altcoin(s) to mine. So it could be better if you must have invested in an altcoins rather than mining, you could do some trading while investing on altcoins. Just fill your portfolio with all of the good altcoins that has a potential to grow in the future.