Hmmm... Nothing like a well thought out follow-up question to get you to fill leaky holes in a previous opinion. Haha!
If I were selling a 240Z, I guess it would come down to the condition of the rest of the car and if I considered it "collectible" or not.
If I thought the car had solid standing as "original", then I could value the original factory equipped transmission higher (regardless if it were a 4 or a 5-speed). By that, I mean if someone could unquestionably prove that transmission was bolted to that motor left the factory in that car on day one, then I would probably consider that trans as having collector "originality" value. But only if the rest of the car supported that situation.
If the exterior had already been irreversibly changed (fender chopped out and flares added, spook instead of original front, etc) and the engine had been changed (someone swapped in an L28 but kept the original trans) and the interior had been irreversibly changed (roll bar), then having the original transmission would mean little to me. In that situation, I would NOT mention the trans being original in a for-sale ad.
Unfortunately, I'm not in a position to purchase a collectible 240Z. Now that the prices are rising so quickly, I guess I missed my opportunity. And since I won't be buying one, I guess I won't be selling one. "Driver quality" only for me, and the transmission thing is low on the list.