Who knows - he may have failed, and never gone on to become a pro-footballer. Or not. A lot of it depends on the timing, and the circumstances. I just can't see how the circumstances here are right to take a punt on someone like Semmy.
As for step-ups, I think there's a difference between Handy Prem and Aussie state leagues. Only three players have ever really gone on to be good players at A-league level: Siggy, Riera, and Krishna. Of those, only Riera was able to slot in off the bat, the other two needed time to get up to speed. That's not really a great strike rate over 12 years of the club.
And even for Aussie state leagues, for every Manny there's a Jimmy Downey, Nick Tsattalios, Reece Caira, Josh Brindell-South, and so on. So the strike rate for players coming for lower levels is pretty low, and when a player in question is an import, the risk is getting a bit too much.
Interesting that you don't rate Cacace.