The answer is that it pretty much depends on the game size. 2000+, I would consider it. Mainly because I do happen to have 5 incubi, and a really nicely converted incubi/incubi master, just cause I wanted something different. Well.. Lets just say they usually don't se a lot of action. But I'm off the topic already. in 1500 and below, not a chance. Probably no in 1750, and a tenative no in 1850.
Pick one or the other, not both. Otherwise you have lots of points invested in very few models, wich is not good. When I play DE (and it doesn't work for other races, so mind that) I usually work the 'rule of 200.' In any game of 1500 points no unit costs more than about 200 points. Thats about 13% of your army in one unit. This way if you loose it, although it might hurt... its not devestating. If you loose that 300 point "One fifth of my strike force" HQ than it is really quite a punch in the face. In case you were wondering, those 200 pt squads are my wych units.
Personally I'm not a big fan of incubi. I've stated my reasons before, and I think it is infinitely better to stick her on a skyboard, or a reaver, or even just use her as an IC and attach her to a wych squad. Basically because if the raider carrying the incubi gets shot down on turn 1, you have a whole lot of nothing for the rest of the game with that unit. At least with the wych raider, the wyches and archon can still fleet of foot.
But it looks like I'm off the subject again. I would go with an Archon with power weapons, reaver, drugs, tormentor helm, shadowfield. Comes out to a beautiful 165 points. If you really want you can put plasmas on her as well, I usually don't, but thats personal pref I guess.
Does it die quickly becasuse of all those attacks? Oh abosloutely. Its hack slash and burn. But there are 2 things you can do about it.
1) Throw some meat into the grinder along with her. A warrior squad works nicely. Then at least some of the attacks pretty much (not always) have to go against the warriors, and not your precious archon. While she dishes out the destruction
2) Simply let it happen. Get a few lucky rolls here and there and the archon will become known and feared as a monster. Then use the psych out tactics with her, throw her at something your opponent doesn't want to die, he will probably overcompensate with rescources trying to stop you, allowing you to hammer him elsewhere. This is what I usually do, though I'm really trying to force myself to use a more conservative appraoach.
As far as an HQ without shadowfield goes... Well it doesn't matter if you have incubi around. The real reason you even bought the lord is so you can take incubi. So if it dies, no big deal, you still have the real damage dealers around.
Looks like I beat around the bush quite a bit, I hope you still managed to reap something out of all that.
Wasp