I believe our maintenance interval for coolant is at 50k. Might wanna call your dealer just to be sure. Coolant flushing helps keep the water pump lubed up. Over time tends to "brown" cuz of rust so you might not want anything like that blocking your coolant passages. So yes, I find it necessary.

 

In addition to the water pump it also prevents the buildup of gunk in the system and keeps the metals from eroding/pitting. I'm not sure what the maintenance interval is but 30k is way too often. Most cars nowadays have 100k mile coolant but I'm not sure about Mazda. Also using factory coolant or a confirmed compatible coolant is a must

 

I believe our maintenance interval for coolant is at 50k. Might wanna call your dealer just to be sure. Coolant flushing helps keep the water pump lubed up. Over time tends to "brown" cuz of rust so you might not want anything like that blocking your coolant passages. So yes, I find it necessary.

MS3 workshop manual, pg38, has the coolant change scheduled for:

FL22 type (MS3): 120k miles/10years, then 60k miles/5years after that.

All others: 60k miles/4 years, then every 2 years after that.

Edit: I looked at the 2012 owner's manual, pg 386, and it's the same as I've listed above.

MS3 manual:

 

Don't they make test strips to test coolant? That way you can find out if you really need to change coolant.

 

I know there are test strips that you can get, though I think it just a waste of money. Just follow the recommend interval and you will be good.

 

I really hate how all of the old service intervals on cars are still advised on newer cars. It wastes so much time and money for people, not to mention all the oil wasted on 3k mile oil changes.

 

@mazdaspeedmyk is right...