Here is a ssystem I have used to pick plenty of winners.
The rules are very simple.
1.The horse must have run a place at its last four starts without a spell.
2.Its last start was at a city meeting in the same state it is now racing.
3.All I do is check out the selections and be sensible about which ones I back.
Try it.
See how you go.

I ran this across the last 2.5 years Saturday in Melbourne and Sydney adding only two extra rules, less than 25 lifetime starts and top 5 average prizemoney earners and came up with nearly 300 bets for about 28% win rate and a marginal profit. As you say they are worth a look if you can wean a few of the losers freehand.
However, I think Statman's Darkhorse system he sold thru PPM was similar but reports by long time users not good.