It kind of reminds me of a similar dilemma brought up in Persona 3 (serious spoilers follow; do NOT open the spoiler unless you've played it or don't care):
To anyone who missed the above: P3's view is basically that sometimes the choice to erase your bad memories seems like a good idea logically, but in doing so you end up losing pretty much everything you care about. If you have your memories things won't be easy, particularly with some of the knowledge you have, but you will always have the people and things you remember that make it worth keeping going in the end because they're important enough to you to shoulder all of the bad things.
So how does FF4 compare? Well. I guess it's not entirely different, given Ruka's role. If she hadn't gone and tried to get her memories back, she would never have stopped Sakuya - intentionally or not at first - and who knows what would have happened to the surrounding area. It's not the kind of curse that just anyone could stumble in and solve, because while there are apparently plenty of folklorists willing to stumble into the jaws of certain death, how many have her knowledge and are as adept at
using bad pointer controls playing keyboards as Ruka? So without regaining that knowledge I guess everyone would kind of be dead by now. They don't really go into too much depth with how it affects her afterwards, certainly not as much as the characters from the original games get, so it's hard to know if her memories managed to screw her up completely, but she seems okay enough. Plus she now has memories of her family that aren't just Sayaka being ill and everything and Souya being an utter sardine, so that's something she can take away from it. Before that all she knew was this one single scary memory of her father and not exactly the best side of her mother after everything that happened, including, uh, her death, so that sounds like a pretty nice trade-off.
I'm not entirely sure what Misaki has to gain from getting her memories back, really. She doesn't seem to have had some kind of family crisis like Ruka, she still has Madoka... so for her it's going to be more "filling in the missing pieces so I know who I actually am" I guess. Unless there's some part of her childhood that's really important that she forgot, all she reaaally has to remember is Sakuya and Miya, and what she specifically gains from this... I don't know. She was friends with Sakuya, sure, but is there something behind this important enough to risk (and possibly lose) her life in order to remember that? Unless she didn't have a mother and this was her only real kind of contact with a mother figure, maybe that might explain it, but otherwise I don't really think so. Surely you'd rather not remember your friend/possible-mother-figure dying (or not) and turning into an evil ghost (or not) before your eyes after having been severely ill, not to mention your own kidnapping and prior suffering due to illness? Doesn't really seem to balance out the rewards.
Madoka obviously has nothing to gain and everything to lose. She now has Misaki all to herself since Miya is out of the picture, she doesn't have to remember being chucked down the stairs, her bird being murdered and merciless bullying by an insane child... It was actually probably a good thing she forgot all of this in the first place. I wonder what she would've turned out like if she did remember everything, given her nature? She surely remembers more than enough already.
Choushirou would have kept going in that loop forever if he didn't remember, so it helps him, and by extension Ruka. Even if he is kind of dead now. Everyone wins. Except Choushirou. Because he's dead.
Good ending: Madoka oversleeps and misses the boat; Choushirou is reincarnated as Ruri and assists Miku with her investigations
Normal ending: Ruka sacrifices herself to the Whirlpool of Dead Anger in putting the mask on Sakuya and dies; everyone has a party in the afterlife except Souya who isn't allowed
Bad ending: Ruka has a severe blister attack climbing the lighthouse from her impractical footwear and never makes it to the top; everyone dies
No but really:
Good ending: I'm trying desperately to think of a way to resurrect Madoka but I can't, and I'm not a good ending person so I give up
Normal ending: Same as the one in the game really (Normal mode)
Bad ending: Choushirou never remembers, never shows up with the mask and continues in an eternal loop forever (;_; ), Ruka Blooms via Sakuya and forgets everything and never sees Souya, Misaki Blooms and forgets who Madoka is, Madoka is still dead,
Martini Monday is cancelled
Other games, just for comparison's sake:
If we're talking post-FF3, it's better for them all to remember. Everyone is dead, yes, but they're better off for what they've all been through, and they have a new branch of Survivors of Evil Ghosts Anonymous. You could say that Miku might be better off after the events of 1 because Christ, Mafuyu, what was that about, Mio hardly functions at all after 2, Rei is Rei... but after 3 they all move on and live for the dead people blah blah blah. Out of all of them, Miku probably would have the most to gain from forgetting, though. I mean, I know it logically works this way but not emotionally and all, but her brother abandoned her for a dead girl. Come on. Really. Dead girl. Mafuyu. Mio, on the other hand... has the most to gain from remembering. She does shut down totally afterwards, but later on when she learns to live with it it kind of sets her free. She's lived her entire life tied down to Mayu and imagine what her future would have looked like. Yes, she loved Mayu, but now she's free to be her own person at the same time as the only way she could truly be one with Mayu - the only thing that would make either of them happy - and that's surely a good thing? Rei, I don't know. She's kind of a different case altogether.
I'm actually a little confused about why Mafuyu is so eager to take the camera along with him when he knows precisely how dangerous it is first-hand. I assume he would have intended to use it on an "only if it's absolutely necessary" basis, but honestly, it sounds like kind of a bad idea. What makes him think the same thing won't happen to him, even if his spiritual power is weaker to start with? Is Takamine really worth that kind of sacrifice? Mio isn't as clued-in as some of the others, so it makes more sense for her to use it the way she does, particularly with Mayu to protect. FF3... kind of more ambiguous, since it's in a dream. Do the cameras affect you the way they do in the real world? You could argue yes, because Rei starts seeing ghosts in her own house, but it's also arguable that it's an effect of the spreading dream and has nothing to do with linking to the camera.
What about Misaki? Did the Asous talk about the camera? Does she know its effects? Surely if she knows how to use it she must do? How did she get hold of it? Why is such a rare and precious artefact just lying about for her to take? Surely she's even more at risk since we know she has powerful spirit power? What is Ruka's like? Does she see ghosts before she uses the camera? Does it actually affect them after they stop taking photos, or do they have that heightened connection for the rest of their lives, and how does THAT affect them? Same with the radio. There's one vague mention of this in FF4 about listening to the radio driving people insane, but when has that ever happened? It doesn't seem to have bothered anyone before. If it was such a niche - and mostly rejected as pseudoscience - pursuit, why does everyone and their grandmother seem to have been driven crazy by it - except the actual people in the games? What about the projector? Does watching too much of that kill you, too? If you watch the Kaname film on a loop do you eventually go bonkers?
this is really long and I have no idea what I'm really talking about anymore and I went off topic hours ago so I'm just going to go ahead and hit post now