Do you ever experience any problems with shifting?
If you don't, and the fluid is nice and pink, and does not smell burnt at all, then this is what I'd do if it were my car.

Flushing is not really the best thing to do, especially with older cars.
I'd just have the fluid serviced, which means have the pan dropped, and the filter replaced, then fill/top it off with Dexron VI, Dexron III and VI are fully backwards compatible, and mixing them will not hurt anything.
By just servicing the fluid/filter you will still retain some of the old fluid, which is a good thing to do given the age of the car.

When you have it serviced be sure to check the pan for and metal bits, and clean off the magnet in the pan, I'd expect to see it have a good bit of greasy/metallic looking goo on it, this is normal, just keep an eye out for any bigger bits of metal.
I like to put my old fluid in a plastic drain pan, and run a rare earth magnet through it, then examine the magnet.

I only have problems with shifting when the engine is cold. When I leave for work or vice-versa, unless I accelerate hard, it feels like it'* hanging in first for a long time before it shifts into second. I'm wondering if I may do more harm than good by changing the filter and adding new Dexron II to it (manual and dipstick call for Dexron II). I was just wondering about the age of the fluid. It'* 10 years old. By the way, what'* the difference between all the Dexrons, detergents added to them? I will probably have to add a little fluid anyways when I install my new radiator.

Dex II is not available anymore. It best to use Dex VI when you service the tranny. It will not hurt anything. If anything the dex VI will be better for the tranny.

The only thing I have heard is the viscosity of Dex VI is a bit thinner, and some say that may cause issues with higher mile/older cars, if they have existing transmission problems, but I am not sure how true that is.
If your fluid is clean like you say, not burnt, and you find no bigger sized bits of metal in your pan, then I'd go ahead and add Dex VI when you top it back off.

I don't know if it makes any difference, but I need to correct myself and say the transaxle seems to bog down in second before shifting to third when cold. Thanks for all of your opinions.