Maybe there's another thread somewhere for this but has anyone discussed that even with so much power of our Antminer S1, it's looking very doubtful that we're gonna get our ROI of 3.15BTC? [I'm not complaining at all; as I suspected it from the start before I bought it

]
You (meaning anyone, not just you) can
not accurately predict ROI since it depends on future difficulty changes, and also on the residual value of the miner. All you can do on these is guess. If you guess that these will be low+high you should buy the miner, if not you shouldn't.
There is this fallacy that you can make a few clicks a on web site like genesis block, etc. and get a definitive yes or no answer on whether to purchase a miner. False.
As for mining some other coin if you look at profitability of mining other SHA256 coins it has generally not been favorable. Mining scrypt coins has been somewhat favorable. But as for the future, again all you can do is guess.