I wanted to know your opinion on everything except that part - If satoshinonce accepted investments, is such a risk entirely eliminated?
Disclaimer: I am not a mining expert, so anyone please correct me if I am wrong here....
satoshinonce would not be fair for investors and that site is technically not even provably fair for the player.
yeah, wtf? I never heard of this site, but they seem to do it in the worst possible way. As you note, it allows a miner to costlessly cheat the site. (miners can have a fixed nonce, and purely fiddle with the coinbase) and theoretically allow the site to cheat players (I doubt this would happen though, if they were sophisticated to know how to cheat players they would realize players can do the exact same attack against them).
Making bets on the last (couple?) digit of the block hash seems a lot smarter, as now miners have to discard blocks in order to cheat, which is rather expensive.