Yes, with brighter lights reflecting off the plates, your multi-exposure HDR would assist with the plate reading. As it is, it doesn't appear to have helped at all. I think the current firmware needs quite bright lights, and they also have to have beams that illuminate the plates, while older headlamps, pre-LED, tend to avoid illuminating the front of the approaching cars, unless maybe they have self-leveling mechanisms.
If the plastic lenses have clouded then give them a good polish with some fine abrasive polish, they can end up like new!
Although you are likely to have to repeat it once a year once the surface coatings have gone.
Loss of light is often due to deteriorated mirror surfaces though, and that is much harder to fix.