is it better to have someone flush your tranny or to just drain it?
Personally, I don't believe in flushes. Others do. So I would just drain it, especially if the old fluid still seems ok (that is, if it's still clear red and doesn't smell burnt or really bad).
If you want more fluid exchange, repeat the drain/fill procedure a couple of times after driving it around a little bit.
I have on 02 with 67,000 miles on it and have no idea if the fluid or filter has ever been changed. I would feel better with a full flush but how much would that be?
There's a do-it-yourself procedure called the "Hoot Method" (seach for "hoot method allison flush"). I don't know how much it costs to have it done (also depends if you want to go with Transynd).
[on edit] Ooops, the Hoot Method also involves switching to a deep pan. You don't need to remove the pan just to do the flush . . . unless you feel compelled to change the internal filter.
also if you change the spin on filter does tranny fluid spill out when the filter is off or what, and if you drain it how much fluid should you put back in?
The only fluid loss is what's in the filter when just replacing it. If possible, measure how much comes out and put that much new stuff back in. Also, others have found that it's important to fill to the middle of the hot range on the dipstick; overfilling causes the transmission to run hotter and possibly overflow.