Phoenix, personally, I wouldn't worry about the total time. I definitely wouldn't do anything to purposely stretch out what you have. Maybe make a few extra side quests or something, if you'd like it to be a bit longer. Don't comprise your original plan just to make a longer game, it's not worth it. I'm sure everyone will love it even if it's only an hour long.
Don't worry, I won't artificially extend the gameplay. I'm reusing all the original location maps, so it should match the original in length at least for that. I'm expanding the dialogue extensively, too, so it will probably end up being longer. Mostly, I just wanted to know how much gameplay I could expect, so I can roughly gauge how much I've completed. It makes me feel like I'm actually making progress.

I don't know about you, but I find games that force you to grind to just be irritating. The original game never required you to grind at all, you could if you wanted to make a few areas a bit easier, but the game was completely beatable if you just fully explored each area and fought all of the random encounters.
That's what I'm shooting for, in terms of playability. I don't want players to have to grind, though I've added a Call command so that you can do it more quickly if you like to. It's not going to be a challenge hack, but I do want it a bit more difficult than the original.
Well maybe it just leeches time doing that way. Maybe if you make the treasure worthwhile enough in each area it gives the user a legitimate reason to explore everything. Maybe minibosses like what I did on my hack?
I'm planning on having a few sidequests with bosses. I like the idea of minibosses -- I'll take it into consideration when I'm coding the rest of the events.