Lyle,
Watchful waiting is definitely rational. After being diagnosed with BX/MAC, because I was , asymptomatic I did airway clearance for 1 1/2 years, three times a day to try to get rid of the MAC. I wanted to avoid the Big 3 for as long as I could because of the potential severe side effects and even if mild effects, they really compromises one's immune system. Unfortunately, my sputum results kept being positive so I've been on the Big 3 meds for four months now. I question whether I should have gone on the meds instead of continuing to do airway clearance. There are studies that show that one can get rid of the MAC through airway clearance though the percentage of people who succeed is not high but it's possible. Unfortunately the lab I use does not do colony counts so there's no way to tell whether over the 1 1/2 years of airway clearance, the colony of MAC was decreasing or not. If the colony count gets low enough, you don't need to be on the Big 3.

I found this talk by Dr. Gwen Huitt at National Jewish helpful about when to be treated with antibiotics and when not to:

To Treat or Not to Treat
Gwen Huitt

Does your lab do colony counts of your sputum culture? Your doctor can ask that your sputum sample be sent to NJH for the colony count. You don't have to be a patient of NJH to get the colony count done at their lab.
Hope this helps,
lora jo