I just went through this process, and found that some programs are more willing to "entertain" scholarship negotiations than others. Typically, based on the advice I got from my consultant, you can leverage an offer from a higher-ranked school to negotiate an offer from a lower-ranked one. (For example, if you get accepted to both MIT and Anderson, for example, you can leverage the MIT offer to try to get money from Anderson - ranked lower). But some schools, as I've learned, are less likely to entertain you if you request a scholarship. I've heard that Wharton, in particular, is tough (I didn't apply there so can't speak from experience). Hope that helps!
I was able to get more money from one school I applied to. I didn't end up taking it, but it was worth trying to see what I could churn up. Best to know you have all your "best offers" from your schools when trying to make a decision, in my opinion.