I asked my vet regarding the titer test. She is always open to my views and didn't say it wasn't a good idea. What she did say what this:

No one has ever found a direct correllation between a high titer count and resistance to a disease. She said that it is assumed but never proven with a "Challenge trial".

I still got my puppy tested and when his titer test came back acceptable I didn't further vaccinate him. But I thought I'd pass along what my vet said.