Those are actually prizes for the 200 cr ones, so even the finalist in the 100 cr 18 holer actually loses a few cr in the end (432 cr prize at a cca 440cr cost, lol). That's why I almost never entered those, unless there was a par 3 course in the mix and I never used anything better than L33 Callies there.
Oops, I suppose paying out 2,880c with 1,600c entry fees was unlikely :-(. So only the winner gains overall and getting to the semi "costs" 226c.
I'm sure you will have found the best way to gain from these but also part of that is winning fairly often, that would be the tricky bit for most of us :-)
As wgt take a lot less from bracket (10%) entry fees than they do from rg's it should be possible to win and, as you also said, you only have to beat four people not forty nine. The insurance is better (100c entry then the top 10 don't lose) and ball use less in rg's though.