I do not bet on Trifecta or First4 (so feel free to ignore this!) but I noticed something yesterday that may be worth considering. Have a look at the results for the Metropolitan (SR6) on NSW. The first 2 positions were filled by "value" runners (Victory Smile at $33 and Piachay at $4.20 the place), the 2nd favourite was 3rd (Dress Circle at about $5 win quote) and favourite was 4th (Red Trinket at about $3.80 win quote).

The Exotic Divs for the race were:
Exacta $358.80
Trifecta $3204.90
First4 $20336.80

Now if you assume that the win price is a close approximation of each runners chances in the race you can work out what the true dividends should be (adjusting the win price to remove the TAB "cut" and then expressing it as a percentage). Doing this you get:
Exacta (7-19) = $565.90
Trifecta (7-19-2) = $3064
First4 (7-19-2-18) = $10083

As you can see the Exacta paid was a big under given the long odds of the runners. The Trifecta was over the true odds by about 5% but the First4 paid double what it should have done as the chance of the favourite running 4th given the first 3 finishers was about 30%.

Maybe there is something to be said for leaving the favourites out of the first 2 placings in your Trifecta's/First4's and including them as the 3rd/4th selection? You certainly won't get many winners but when you pick one up it will probably be a good payout.

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"Computers can do that????" - Homer Simpson