Master Air Flow Sensor, Synthetic Oil, Fuel Additives

1997 Mazda 626 LX 92,000 I have several questions that I should like to know about please. 1. I have had several mechanics recently say to me that I should be using a synthetic oil because of the miles
and the age of the engine along with a different oil filter. I was under the impression that Mazda does not think so and strongly advises you not too, I would like to know why? 2. The same goes for adding anything to your fuel tank? 3. This is a biggie, for the past 5 months I was having trouble with my car, I could be going on the highway and doing 60-70 when maybe I need to accelerate, well the car would like suddenly die on me and go down to 40-30 and felt like it was going to just stop. I would let up on gas peddle and it would slowly go back up but the rpm jumped from 0-2000,3000 and it felt like the transmission was going to drop right out, pretty scarry, and had rough idle, and when I was at a complete stop and went to accelerate it would just die sometimes. Long story short, a mechanic told me
the 2 cats and 02 sensors were bad? Someone else suggested it was not that but Master Airflow Sensor. He removed it, cleaned it and put it back. Oh, my check engine light was on the whole time. Now engine light off for 1 whole week, and the car is like new! Does this HAVE to be replaced or will what this wonderful mechanic did last me for awhile?
Also, are there more than 1 maker of this part and is there any difference for future referance? One last question; I live in a climate where it is very very dusty and 4 mos of the year temp gets to 100-119 degrees is there anything that I should be doing to make sure I have no inexpected surprises. I did put in a new radiator, have changed transmission fluid 3xs, timing belt, 1 cat, and 1 02 sensor, upstream at 69,000 and 82,000 mi. Thank you for your assistance, Suzie