I realize that simply draining and refilling your ATF does not remove all of the old fluid, but if your tranny is in good shape and has been well maintained otherwise; is there any reason why you should go for a flush (of fluid exchange) instead?

 

Flushing the system is good( if you don't have a tranny filter) because it removes all the old fluid from transmission lines and cooler, you don't want to contaminate the new fluid. If your car has a tranny filter its not recommed to have a flush because the old tranny filter is full of old fluid and contaminates.

 

Over the years I've been following this whole Tranny Flush vs. Tranny Service debate, and I have to tell you, more often than not, those who've opted for the flush end up opting to buy a new transmission a few thousand miles later. Fastest way I know of, of effing up an automatic transmission.

Save yourself thousands of dollars and have it serviced the way Mazda recommends you have it serviced; drop the pan, change the filter, put the pan back on, and fill're back up.