I haven't noticed any of the symptoms being discussed, though I'm lucky to have a tube with perfect emissions on all three guns so it's pretty easy to get a bright image without taxing the HV supply.
Again, it's important to set up the horizontal and HV regulation circuits correctly. When doing a set, I always test the HV unloaded with the regulator disconnected to see where it tops out. My CTC-2 makes about 22.5kv, so I know it will easily make a stable 20kv with the regulator tube doing its thing. Other sets are not as good, my Wingate struggles to make 22.5 with no image on the screen and the regulator cap off. My CTC-4 on the other hand is absolutely leathal, I'm not sure where it topped out at since it overloaded my probe but WAG is around 38-40kv? They can be all over the map.
Tom: if the filaments are being affected too much, you might consider taking the filament windings off the flyback and moving them to a step down transformer. Take a 120v primary transformer from something small like a clock radio, and remove the secondary windings. Replace those with a few turns of HV wire and run that to the rectifiers, the current you save won't have to come from the flyback anymore and may just give it the oomph it needs to make respectable pictures again. You could test the theory by temping in some 1.5v batteries to power the rectifiers, if it doesn't help at least you didn't spend any money. Just a thought.