I agree about "Ineffective" Lizard Dude. I enjoyed the older version more, as it was more difficult. Battles were more interesting as you had to plan out your attack, instead of just how many times you need to hit the A button.
Bird Person, the GBA and the PSX versions of the game are different. Very much so. They have their similarities, graphics and music (The PSX's music is of better quality, but the GBA does a nice job), and the difficulty is indeed lessened for the GBA version. Prices of items and magic differ, and more importantly the whole Magic system was changed to the MP system. That's a massive difference between the NES/WSC/PSX and the GBA version. You don't have to believe me, but I assure you I am not telling you any lies.
The changes I listed were really just a few things that I could remember that I felt affected gameplay and difficulty. There are plenty of changes between the Japanese and English versions, and if you're really interested you could investigate it further. A few more that I can think of (For trivia's sake) are that in the English version, the "Eye" monster in the Ice Cave was changed. There's no real reason for it, but they're different. Crosses were changed to candles. Names in general, as spells, monsters and items were changed. And in Elf Land, or Elfheim in the more recent translations, the tombstone near the entrence read "Here lies Erdrick." (The hero from Dragon Quest/Warrior) in the English NES release. In the Japanese version, and the more recent English translations, it reads "Here lies Link."
Eh, there's plenty more I'm sure, but that's all I'm coming up with at the moment.
Also, HARM wasn't Holy. HARM is the equivalent to the Dia spells. Holy was FADE in the NES version.