Hi! I love this project and saw that I was mentioned re: Phantasy Star II. Wanted to chime in that while I did 4x exp/meseta for it, there's probably certainly value in a 2x patch also. Degrees of difficulty, and all that.
Regarding Dragon Warrior III: The US NES version of DW3 has a routine hacked into the end-of-battle code (or something like that) that applies an artificial multiplier to EXP gains already (I don't think money is affected). So if you search for the EXP values you see in game, you won't find anything - the monster data still has the unmodified EXP values from the Japanese version.
Unfortunately, I don't remember exactly how that code works. You might try poking zombero though, he's done a lot of internal meddling with DW3.
Regarding FF3: Yes, definitely double job EXP. (Note that Job EXP and Capacity are not the same thing!) There's also a hidden melee proficiency stat detailed in the game mechanics FAQs for the game which should be doubled. (I know it's explicitly mentioned in the DS version's mechanics FAQs, but I'm not sure about NES; nonetheless I think the mechanic exists in both versions.) In short, this game has a lot of hidden advancement crap just like FF2.
Regarding FF5 and FF6: Did you double ABP/Magic Points also?
Regarding FF2: A reworked FF2 to have traditional leveling would be an extremely ambitious project indeed, but I think it has a lot of potential to be very interesting.