Where you notice the gains from the DV+ is throttle response. As the second spring closes the valve as soon as is possible, even though the ECU would hold it open for longer than needed, it means the boost pipework fills with air that much quicker, meaning you're on boost quicker.
That, as well as a much smoother transition between vac and boost when you're driving and tickling the throttle ( motorway cruising for example). Be warned you will likely get an underlying fault code telling you the DV is not doing its job properly, but thats because of the effect of the second spring. No EML appears