I'd really like to have Imoen in my party, for RP puroses, but Nalia (if taken right away in Chapter 2) will always be at a higher level of experience, and the powergamer in me can't give that up.

Has anybody ever had both of these ladies in the party at the same time? How did it work out?

One suggestion would be to use the Level 1 NPC Mod from Gebhard Blucher (http://www.fortunecity.com/boozers/winelodge/79/) to have Imoen become either a full thief or a full mage. I prefer her as a swashbuckler myself. That way, Nalia can fill in as mage and Imoen as thief.

I've taken them both once or twice but depending on the structure of the rest of the party, it can be somewhat overkill. While my preference has always been to take Nalia, it all largely depends on your preferences.

Both are more than capable of handling any traps or locks in the game without any assistance (rings, potions, etc) and both are capable of achieving high levels as mages. There is the odd occasion that a trap is too difficult for either of them but then that's one reason why you have summoning spells -- to have them set off traps.

Depending on when you pick up Nalia, and when you set off to get Imoen, she will always be one or two levels above Imoen. All a matter of how you play and your party design. Personally, I find two mages a bit overpowering and while they may make the more difficult encounters easier to handle, it takes away some of the thrill as well.

Nah, I'm really not into mods. Thank you, though. I think I'll give the mage duo a shot anyway. :)

I usually just take Imoen, she's just way better as a character and more important to the story.

You could always save most of the quests until Chapter 6. It's more than possible to get either Nalia or Imoen to 3 million xp by the Tree of Life fight.

Nalia may actually be lower than Imoen if you only do enough quests to get the 15k gold.

Imoen is only important to the story to the point of her rescue. Once that is accomplished, her significance to the storyline disappears.

What about recovering her soul? I'd say that's pretty important to the plot.

Yea, but she gets that back regardless of whether or not she is in your party.

By all means take them both. I've always felt one mage was never quite enough and if you're not going to take Edwin with you I can't see a reason why not to take along both Imoen and Nalia.

I've taken them both on more than one occasion, and though I had to sleep a bit more bringing two mages that can reach 30+ level along is definitely overkill. (Hardcore-wise)
I doubt the same is true in harder difficulties, though. In my games Nalia had the nasty habit of getting hit by her own fireballs. ;)