The friction modifiers aren't all that different. The given HFM level is. But, most transmissions work within a reasoably wide range of HFM level. This is why multivehicle ATFs and aftermarkter fluid converters work extremely well.
This is also one reason why OEM's can back spec better fluids as improvements to older transmissions.
Older transmissions are less dependent on HFM level then the newer electronically controlled slip-shift and/or variable torque converter lockup type transmissions. I doubt that a '92 economy car has either.
There is nothing wrong with using DexronIII in place of DexronII. All the stories you hear are hearsay. These are equivalent to the stories that ATF flushes caused failures, synthetics cause seal leaks,....... All issues are caused by factory defects, owners negligence, and owners abuse.
Not knowing the previous maintenance history on this thread starter's vehicle, I would definitely use the Z1 ATF. The reason why isn't because its the best, its because the fluid won't be blamed for the failure if there are any issues currently unknown. A 15 year old transmission, regardless of the low mileage, will have issues. And, most owners look to point failure blame elsewhere and not at themselves.
I do recommend a full flush with ANY decent ATF. After that, a yearly drain/refill or 2 would be plenty. Blended and full synthetics are recommended. And, an HFM'd fluid or additive can smooth a shift a little, especially in a simple shift-point programmed transmission. But, don't expect any additive or fluid to rebuild the transmission.
$4 doesn't sound like much for OEM fluid. But, thats just $1 fluid with profit margin. Sorry, but I just don't see the need for it when DexronII was an acceptable choice in '92. And, most synth blend ATF are in that price range with better performance.
Valvoline Maxlife would be an easy choice. It works well in brand new hondacuras so it would be a smoother shifting upgrade to an older Honda. It is not overpriced, available in most autoparts and department stores, and is a highmileage ATF which would be a good match for a 15+ year old unknown history transmission.
