Eldo - How many miles do you have on your car? In my experience that's the biggest deciding factor on if you change the fluid or just let'r ride.
At the shop here we recommend skipping it if you're over 100k, because at that point you're getting in the area of more risk than reward. As it's been explained to me, The worry of a high mileage fluid change is that the fresh load of detergents in the new fluid could potentially wipe out the worn friction plates/bands in the tranny. Especially if done via flush machine as mentioned.
My own car I've been doing about every 60-70k for transmission services (fluid drain + new filter). Does it really lengthen the life of the trans? Don't know for sure, but I'm an over-maintainer. (Synthetic oil changes every 5k). But, car's got 20_,___ on it now and no one believes it when they drive it.