It's a good idea, since FF games, even though they're wonderful, lack more difficulty. I agree with Big D; it's not neccessary to increase the HP a lot; I mean, it doesn't make sense that a human enemy has way more HP than giant monsters. I think the key to make the game harder is setting levels and increase the stats. What was Edea's HP in the 2nd disk? I think it's about 16,000, not bad at all. The problem is that she has a weak physical defense and their attacks, except Maesltrom, weren't really impressive.

The problem with making a harder game though, is that some gamers would get stuck and it wouldn't be so popular. In short, they would probably sell less games.