does my car require a fuel injection cleaning every 30000 miles?

I gave my (new) 2015 Mazda an injector  cleaning at 80K.  I had No record if it ever had been done. It  now accelerates a lot better (new plugs, too, there were overdue by 10k)   Had good MPG but a flat spot from 15-30 MPH. I am running cheap Charlie regular in it so I wont be surprised if it needs another in 30 K or so. I used to get my '91 cleaned every year, regardless of miles or hours on engine.

I doubt it's needed. gasoline is so highly refined now that the only way your fuel injectors are going to get dirty is if you let it sit for a year with old reformulated gasoline. 

He may be right. Kia may have published a service bulletin due to carbon build up on the backs of the intake valves. Direct injected engines are prone to this because there is no washing effect from fuel being sprayed on them. Injector cleaner in the gas really doesn't help because of this.

Many manufacturers now recommend removing the intake manifold periodically so that the backs of the valves can be blasted with nutshells to remove the crippling carbon build-up.

i would do what your mechanic told you to do