If they aren't *cursed* they're perfectly fine for champ spawns and routine hunting. A few people don't like the area effect because they say it aggros everything around, thus overwhelming you. While this makes it a bad pvp choice, in pvm, those monsters around you would probably aggro on you anyway. I would like to note that Talisman Slayers (Vermin, beetle, bird etc) also apply to area damage effects. 100% poison area will help you kill more faster, especially against your equipped slayer tali targets. Serps Fang is 75% poison damage and some things have very high poison resist (I saw your eyebrow raise when I mentioned beetle slayer LOL), but you can work around this by wearing a quiver to modify your damage or Consecrate Arms. Fencing weapons don't really have obvious choices for normal hunting; the Blackthorn Krysses are expensive and not very flexible, as you need all six to be prepared. The Fang has the base of a good general pvm weapon: max HCI, a damaging effect, high DI and its naturally fast (2s). Its special attacks are Armor Ignore and Infecting Strike, both very good moves.
Some Fang uses you may not have thought of? Travesty: The guy with the Fang aggros her spawn lures it off and dies in a corner so you can finish her without 80 ninjas harassing you. Champs: Tank with a Fang aggros teir 1/2 spawn thus letting the necros wither and the mages earthquake without being hit. Teirs poof in a few minutes. The Rat Mines: Low end, but you'll make a ton of gold and arrows here quick, cheese wheels weigh less than fish steaks, and you might get a minor now and then.
Getting a Doom arty means fighting and probably dying to Gauntlet spawn. 250K isn't asking too much at all, especially if you just want one particular item without the bother of Dooming for it and Gold skulls are going for 200K now anyway (Astronaumical price IMO). Compared to Heart of the Lion, Invuln Shields, Boomsticks and other minors that go for the same price or more and are much easier to get from Peerless loot, paragons, Tmaps (lev 6), leviathans, and ML named monsters, the fight to get a Doom arty involves more resources and time without the benefit of making additional gold while you earn them. Thus I arrive at 250K for the respectable Serps Fang. Other less functionable artys (Insight helms, Bonesmashers, Dragonslayers....) might get you 50K at the very max because they're totally unusable in any combat situation.