Harem doesn't fit with the theming for either victory or treasure cards.
It doesn't even have any reason for providing you with money, which is a big negative given that the card's whole gimmick was being a Treasure-Victory card. Not to mention that at the time Intrigue was released, Dominion was still limited to medieval Europe, making a Middle Eastern harem out-of-place (although this changed with Seaside, and the game now spans roughly two millennia of world history, from the classical era to the colonial era). I've often thought of remaking my copies into something more thematic like "Relic" (before that became an official card) or "Jewels" (which is admittedly bland, but in keeping with the vanilla treasures it resembles---like precious metals, only more showy and less practical for spending).
Now that I think of it, Relic is pretty bad, too. The treasure part fits, but since when do relics zap your enemies outside of Indiana Jones movies (though in those they're more likely to zap the user for irreverence, now that I think about it)? Even if you believe the stories of relics performing miracles, they're usually benevolent things like healing rather than anything aggressive. Really, Amulet and Relic could use a name swap (and new art for Relic; it looks like an ordinary necklace---even a gilded box containing the relic would be better). A valuable magic amulet that zaps people makes sense, as does a relic that can earn you money or provide trashing (which already has religious theming---donations? absolution?---with cards like Chapel and Bishop).
I would also nominate the entire category of terminal draw cards, which never settled around a coherent theme like cards that increase your Actions (population) or Buys (commerce). Sure, there are plenty of exceptions in the other categories, but at least you can see a theme, whereas terminal draw cards have virtually nothing in common (Royal Blacksmith is a nice callback to Smithy---and to Grand Market, for that matter---but that's about it).
There's also Woodcutter, as noted by Donald X, but at least it has the excuse of dating from a time when +Buy was called "+Build", which would have made it thematic.