DISCLAIMER: In this post, I am not at all arguing that Nalia inspired Anders in any way. I doubt the writers came as far back as Baldur's Gate for inspiration, and if they did, I doubt they would go to the neglected NPCs of the game, of which Nalia is undoubtedly one.
Does Anders strike anyone as quaintly familiar insofar as his character template is concerned? I have just completed Dragon Age 2 for the first time, and I can say with all honesty that similarities between himself and Nalia (one of my favourite characters, as plenty of you are reluctantly aware!) are fairly obvious to one who wishes to compare and contrast the two.
Both characters are Mages, on a simplistic level. Moreover, both characters intend to use their elevated social status (Nalia - her social class, Anders - his unique place in society) to forward his/her own political manifesto. Anders, naturally, has much more detail and attention paid to his character, but I can't say he is any less overwhelming or persistent than Nalia in fronting his political agenda through dialogue. Anders is much more experienced than Nalia, and thus I must reiterate I do not think that they are mirror image characters, merely that they bear striking similarities. I would say, however, that given his level of detail, Anders is a much more likeable character than Nalia, but if he were transposed into BG2, the character he draws the most similarities with is indeed Nalia.
Nalia is not stupid - that ought to be said, for most people misinterpret her. Certainly she is naive, but her conversations with Viconia and Haer'Dalis (and others, though they do not immediately spring to mind) show that her beliefs stem from an intellectual place as well as an emotional one. She is not carried by whim. To Viconia, she will try to explain that her political beliefs include insisting upon 'an equal distribution of goods' (socialism, essentially) in Amn, which has excess resources to distribute. To Haer'Dalis, she will chastise him for attempting to patronise her. Similarly, Anders will scold and shrug off the other NPCs in DA2 who try to mollify him or belittle his beliefs.
By Throne of Bhaal, Nalia shows an inclination towards her magical power and an interest in acquiring greater strength in order to forward her aims. The morality of her statements are very ambiguous, but in her own context, it is not unfair to suggest that she might move somewhere towards an 'Anders-esque' territory of aligning herself with questionable entities and artefacts in order to forward her agenda.
Again, I will insist that I do not believe Anders is directly inspired by Nalia. I do think it might be interesting to shine a light however on the poignant similarities between both characters - and the sharp contrast in popularity that can be seen between them, which, one might argue, is entirely down to the amount of developer resources committed to the expansion of their individual questlines and dialogue (Anders being favoured greatly in DA2, and Nalia being neglected somewhat in BG2).
Once more, I hope you enjoyed the verbose read guys!