I agree about the checking for a tick disease. In fact, I would consider running an aggressive course of doxycycline even if they are negative, if you can't find anything else.
I would also ask for a copy of any of the bloodwork, and look yourself to see if some of the values are at the high or low portions of the normal range, or even out of normal. I have had dogs with abnormal bloodwork that the vet has said was fine before.
When my boy had some nasal issues, we did do a flush, and it helped him for a couple of years. We were hoping that she would find something to culture, but there was nothing. However, it helped him a lot.
I agree with HRP, when deciding what tests to run, it is important to take into account what you will do with the information. With nasal issues, there are a lot of things that might be done (including CT scan), which we never did. My boy didn't have nosebleeds, but we did suspect a fungal infection, and being a breed susceptible to fungal infections, we treated for that, and he did get better.