I admit I have little knowledge on the UK court system.
However - my only question is - what damage occurred and is that an important metric to prove in order to win a case.
This trial is in the UK so different rules are likely to apply. For example, in the USA you would have to prove a loss but from the article, we have this "The Claimants' application to rely on ground (9) in relation to the DPA [Data Protection Act] claim is allowed." so the plaintiffs' case appears to be built on Google violating the Digital Protection Act which appears to be a United Kingdom law. This would be why Google wants it to be tried in the USA so they need to prove a loss and the DPA would not be applicable.
That said, one could argue that their is a loss. While the information taken by Google may have no monetary value to the plaintiff, it does have monetary value as it is used by Google to increase their ad sales. Without the data, the click through rate is lower. Hence, the value would be the difference in the ad revenue for a group that had the information collected versus the ad revenue for a group that did not have the information collected. The information is worth a lot of money as you can see from Google's advertising sales. Without advertising sales, Google is nothing.