Campagnolo Ergopower Chorus 9 inaccurate shifting
The Ergopower shifters have a part called G spring that eventually wears out. The symptoms are inaccurate shifting and less sharp clicks, just as you are experiencing. The part is still available, not expensive and relatively easy to change.

I would not replace the shifters with Xenon, as it is generally much lower quality and doesn't allow downshifting multiple cogs at a time like other 2000s Ergopowers.