I once proposed something in the TES general discussion about what might improve the "social" challenge of the game.
The idea is to have, on one side, different dialogue tones and, on the other, different degrees of sensitivity.
For example, talking intimidately would work well on a coward NPC.
The principle is to have, as in DF, the option to leave the basic neutral tone to use different tones like :seduction, admiration, kindness, roughness, intimidation, agressiveness. Maybe using those tones should be based on a combo of speechcraft and a stat (like intelligence for admiration, STR for aggressiveness...)
Each NPC will have a set of "defense values" against each of those various tones.
Before talking to a NPC or before asking question about critical subject, the player should think about who he is talking to. Maybe asking other NPC, or talking about secondary topics may help to test a NPC sensitivity.
To add an other layer, the idea is that all the dialog options and infos a NPC may reveal will be set with a level of confidency. Casual questions will be easilly discussed with most NPC while secrets will be hard to discuss about. Some NPC being more talkative than others.
The PC reputation/fame/infamy may affect this level of confidency.
The speechcraft skill will both be taken into account to test a dialog entry success with a classical test, and to assess how the dialog exchange affected the PC reputation toward this NPC. Naturally the PC reputation should not be visible to the player and it would be better if NPC could answer to failed test in a ambiguous enough way so that the player may not always understand he failed.
A second use of the speechcraft skill may be to make an automatic test of a NPC tone during dialogs, suggesting to the player that a NPC is sincere or lying, emotive or neutral.
To finish, as in FO3 (or planescape torment), I'd like to be given more dialog options based on the PC skill set or his stats.
All this should make dialogs a bit more challenging, give the speechcraft skill a clearer use, and give each new character a different potential way to interact with the game world.
At least, I want some social challenge in the game. Entering dialog should be a test of player intellectual and social skills, as well as a place where who the character is will be important.