Interesting angle. Very opportune for me as I was just having a web scraper updated for the oncourse bookies data. I had added open price rank, Fluc count,SP rank. Now I have added price difference, rank difference and probability difference. I am noticing that although there there may or may not be a price difference, the probability has altered differently as the market has come from a 145% opening market down to a 120% starting market. To get the probability difference I converted to 100% in both the OP and SP market. Very early days yet as I am just using the trial version but a simple scan is showing things in a clearer light.
To the point, you may want to consider adding more if possible before you start the download and analysis stage.