My first thought reading this is, like Daniel4; post #20 above, is hand position while riding. It appears all your bikes are drop bar bikes so Daniel's observation re straight handlebars may not apply, but I concur with him that having my hands with palms facing each other is the most natural position for my hands and wrists.
I never gave CTS a thought on the bike. (I do have problems with keyboards and made a pipe insulation palm rest for mine years ago that works well.) But it may not be coincidence that I set up all my bikes to be comfortable riding in the drops before I even start thinking about other hand positions. Modern setups, brifters, ergo HBs, etc. encourage hand positions that don't work for me and discourage the ones that do work. I do like big, long brake hoods and now have V-brake levers on my two good bikes partly for that reason, but I have them rotated further forward and down than most like. This does two things. It rotates the thumb side of my hand forward which is probably a plus CTS-wise and the hoods aren't the ultimately comfy place to park my hands for an hour. Also means that my wrists are relatively straight when I come out of the saddle and pull forward which is how I climb. (The real reason.)
Look at your hand positions. You've been riding 18 years. Positions that are just off might take that long to show up as problematic. And as we get older, what used to work (sorta) stops working. I'm 9 years behind you, but I have also been riding more than 4 decades. (I also benefited from advice from coaches and race veterans, a lot of which has been "debunked" in the years since. I'm seeing my body change and its ability to tolerate the so-so decline. And I am watching myself go back to some of the old ways of doing things that worked for nearly a century. (Laced cycling shoes after a string of foot infections from riding aggressively in shoes with straps. Exact same shoes. Just cut of the straps and install grommets. $10/shoe after doctor's visits, antibiotic routines and many pairs of expensive shoes.)
Your CTS issues may have a cure as simple as my shoes. As I said above, my guess is simply a hand position that maintains your wrist at a different angle. It might cost as much as a new set of HBs, brake levers/brifters, tape and cables. I doubt just cushioning is going to be the cure. I tried various paddings under my shoe straps. It was redistributing the forces over my entire lumpy, bony foot evenly that made a huge difference.
Ben