As much as i know, you will need to just balance your wheels. The alignment only affects the vehicles wheel positions. I was sold by the guy at supaquick that even if i change the mags, i dont need to re-align my vehicle if it is still fine.
A set of tires cost a lot of money and proper wheel alignment will increase the lifetime of the tire and enhance road holding.
That being said.
My car only needed the wheel alignment ADJUSTED on my car after 65 000kms. Usually if you hit something and the car is noticeably pulling to one side or you see the front tires wearing unevenly then you need alignment.
It also depends on the car, a 130 Tazz vs a C63 AMG.