Punters who work with sectional times may well be better punters than those that don't. But that doesn't prove their relative advantage comes from the STs, per se. IMO, it's more likely due to their better knowledge of current form.
Individual sectional times tell us things that get us excited: horse A ran his last 400 in 1.23 sec faster than Horse B, even though Horse B won the race etc. That's all fine, and applies to the particular race, run at the particulat speed, on that track, under those track conditions, etc. Those horses might never meet again. If they do, it's likely that the variables will all be different (distance, track, etc).
To me, the law of diminishing returns comes in quite early when one considers the amount of effort we can go to in collecting (and analysing) sectional times. And as mentioned elsewhere, the trick is to get STs that are accurate. Anyone can kid themselves that they can get accurate times from watching a video, but the reality is they'll have errors of at least 1 sec either way. The only STs that are potentially accurate are those generated by the chip technology used on the southern metro tracks. (I understand they, too, have had technical issues from time to time.)
I'm happy to work with the overall time of the race, and then with the knowledge that horse X gave the winner 4 lengths from the 600, but got beaten just 1 length. That information alone - coupled with an opinion as to the abilities of the horses involved - is all that's needed for future form analysis.