I was doing the same and have seen the occasional thing where one disease was low which I then re-vaccinated for. However, I heard recently that detectable titers aren't necessarily an indicator of whether your dog is or is not immune or could mount an immune response if necessary, it has more to do with whether the dog has been exposed lately and has circulating antibodies. I'm gathering then that high or good titer levels mean good immunity but low titer levels don't necesssarily mean bad immunity.
On the other hand, I haven't researched this myself yet so I may be way off here. Anybody know more?
I think my current plan is to titer for rabies purely to stay in compliance with state laws and avoid the (ridiculous) yearly rabies vax that KY requires but will probably forgo the rest and move to a every 4 year protocol on my older dogs with a known vaccine history and stop vaccinating altogether after a certain age. I foster a lot of dogs straight from shelters and I assume my dogs are at elevated risk of certain diseases compared to other people's pets but knock on wood, I've never had my dogs contract anything and I do use common sense quarantine and disease control practicies. I plan to continue to vax for kennel cough though, which titering doesn't cover anyway and which seems to have a shorter efficacy period.