Multiple endings do not add to replay value at all. If the game sucks, I'm not playing it twice. I play numerous games in which I'm happy enough to get just a "Game Over" screen every single time.

The endings are only interesting if one is not deemed the "true" or "good" ending, because an ending being "good" is subjective. If all the stupid characters being killed off is the "bad" ending, I'll tell you otherwise.

The only visual novel/adventure game I ever played entirely through was X-Change. All the endings were only in part useful enough to the end game percentage. If it's not 100%, I'm usually not pleased. How much I saved the game right before making any of the decisions only to reload it later was the only incentive to play it again. I think I remember two of the five(?) endings the game had. Replay value is at zero.

Wario Land 2 had around 6-ish endings. They were all based off of a branching level path which could be selected if you figured out the proper route to take in each level. The endings were only so much as filler to obtain 100% level completion. If there was only one ending, I still would have played all the levels. Replay value is still quite decent.

Many shoot-em-ups have multiple endings depending on which character you pick, how you played a level and/or if you beat it without continuing usually referred to as 1cc or 1 Credit Completion. The endings, if I even remember what any of them are, are filler. StarFox 64 had multiple level branching and a different final boss if played by level requirements. Of course, it still has zero replay value to me. Castle Shikigami 2 on PS2 still has replay value, despite me not even knowing what anyone in that game was even talking about. The same goes for Touhou Project. The only story/characters I even remember are in Embodiment of Scarlet Devil, because the fandom/fan games seem to push that one in your face the most.

Cave Story has a good replay value to me. The only thing is that I got all the endings once, and there is no incentive to get any of the other ones again as every play-through *must* get to Ballos every time to consider it complete. The same goes for Castlevania. I looked at the ending once, that's good enough; time to meet the requirements for the "true" final boss every single time.

If I already got all the endings, but I always have to do the same final boss/whatever, then what incentive is there to a get an ending I already got, and why pull the extra strings to trigger an optional event that I've already seen?